The effect of knee flexion angle and application of an anterior tibial load at the time of graft fixation on the biomechanics of a posterior cruciate ligament-reconstructed knee

Global variation in isolated posterior cruciate ligament reconstruction

Purpose

In the setting of persistent instability or failed non-operative management, surgical reconstruction is commonly recommended for isolated posterior cruciate ligament (PCL) tears. The purpose of this study was to systematically review published studies to evaluate regional variation in the epidemiology of and surgical approaches to primary, isolated PCL reconstruction.

Methods

A systematic review was performed in June 2022 to identify studies examining operative techniques during primary, isolated PCL reconstruction. Collected variables consisted of reconstruction technique, graft type, graft source, tibial reconstruction technique, femoral and tibial drilling and fixation methods, and whether the remnant PCL was preserved or debrided. Studies were classified into four global regions: Asia, Europe, North America, and South America.

Results

Forty-five studies, consisting of 1461 total patients, were identified. Most of the included studies were from Asia (69%, n = 31/45). Single bundle reconstruction was more commonly reported in studies out of Asia, Europe, and North America. Hamstring autografts were utilized in 51.7% (n = 611/1181) of patients from Asia and 60.8% (n = 124/204) of patients from Europe. Trans-tibial drilling and outside-in femoral drilling were commonly reported in all global regions. The PCL remnant was generally debrided, while remnant preservation was commonly reported in studies from Asia.

Conclusion

Surgical treatment of isolated PCL injuries varies by region, with the majority of published studies coming from Asia. Single-bundle reconstruction with hamstring autograft through a trans-tibial approach is the most commonly reported technique in the literature, with males reported to undergo isolated reconstruction more often than females.

Level of Evidence

Systematic review, Level IV.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40634-022-00541-4.

Low posterior tibial slope is associated with increased risk of PCL graft failure

PURPOSE

To evaluate the effect of posterior tibial slope (PTS) on patient-reported outcomes (PROs) and posterior cruciate ligament (PCL) graft failure after PCL reconstruction.

METHODS

Patients undergoing PCL reconstruction with a minimum 2-year follow-up were included in this retrospective cohort study. A chart review was performed to collect patient-, injury-, and surgery-related data. Medial PTS was measured on preoperative lateral radiographs. Validated PROs, including the International Knee Documentation Committee Subjective Knee Form, Knee injury and Osteoarthritis Outcome Score, Lysholm Score, Tegner Activity Scale, and Visual Analogue Scale for pain, were collected at final follow-up. A correlation analysis was conducted to assess the relationship between PTS and PROs. A logistic regression model was performed to evaluate if PTS could predict PCL graft failure.

RESULTS

Overall, 79 patients with a mean age of 28.6 ± 11.7 years and a mean follow-up of 5.7 ± 3.3 years were included. After a median time from injury of 4.0 months, isolated and combined PCL reconstruction was performed in 22 (28%) and 57 (72%) patients, respectively. There were no statistically significant differences in PROs and PTS between patients undergoing isolated and combined PCL reconstruction (non-significant [n.s.]). There were no significant correlations between PTS and PROs (n.s.). In total, 14 (18%) patients experienced PCL graft failure after a median time of 17.5 months following PCL reconstruction. Patients with PCL graft failure were found to have statistically significantly lower PTS than patients without graft failure (7.0 ± 2.3° vs. 9.2 ± 3.3°, p < 0.05), while no differences were found in PROs (n.s.). PTS was shown to be a significant predictor of PCL graft failure, with a 1.3-fold increase in the odds of graft failure for each one-degree reduction in PTS (p < 0.05).

CONCLUSIONS

This study showed that PTS does not affect PROs after PCL reconstruction, but that PTS represents a surgically modifiable predictor of PCL graft failure.

LEVEL OF EVIDENCE

III.

Second-look arthroscopy after double-bundle posterior cruciate ligament reconstruction: Effect of patient age

Purpose

Second-look arthroscopy is invasive but still one of the most useful postoperative evaluation methods since graft morphology including graft tension, graft tear, and synovial coverage can be directly evaluated. However, only a few studies have evaluated transplanted posterior cruciate ligament (PCL) grafts. This study aimed to clarify the PCL graft morphology and chondral damages at second-look arthroscopy after double-bundle PCL reconstruction (PCLR) and to investigate the effects of patient age on these arthroscopic findings.

Methods

This study retrospectively included 26 patients who underwent second-look arthroscopy at the time of hardware removal 14 months after double-bundle PCLR for isolated PCL injury from January 2007 to December 2020. The patients were divided into two groups: group A, 39 years or younger (n = 14); and group B, 40 years or older (n = 12). At second-look arthroscopy, the grafts were evaluated based on tension (taut, graft tension as tense as a normal PCL; lax, graft tension looser than a normal PCL, unclassified, completely torn graft), tear (one or more tendon strands torn), and synovial coverage (good, synovial coverage greater than 80% around the graft; fair, synovial coverage greater than 50%; and poor, synovial coverage less than 50%). The chondral damages were evaluated using the Outerbridge classification system. Radiographic posterior tibial translation with gravity sag view as well as clinical outcomes were also evaluated.

Results

Anterolateral (AL) graft tension was lax in 8% of the patients, whereas posteromedial (PM) graft tension was lax or unclassified in 24% (p = 0.043). Graft tear was observed only in the PM graft of 19% patients (p = 0.022). Synovial coverage of AL grafts was good or fair in all cases, whereas that of PM grafts was poor in 28% cases (p < 0.001). Regarding the effect of patient age, the synovial coverage of PM grafts was significantly poorer in group B (p = 0.033), but no statistical difference in graft tension or tear was found. The chondral damages were significantly advanced in group B (p ≤ 0.01), except for the trochlear groove and lateral femoral condyle. No patients had residual subjective posterior instability, knee swelling, or loss of extension exceeding 5° or flexion exceeding 10°. All patients had improved from grade II or III preoperatively to grade I or grade II in the posterior drawer test. The posterior tibial translation significantly improved from 10.0 ± 3.6 mm preoperatively to 3.6 ± 2.1 mm at second-look arthroscopy. No significant differences in the postoperative clinical outcomes were observed between the two groups.

Conclusion

The morphology of the PM grafts at second-look arthroscopy after double-bundle PCLR was poorer than that of the AL grafts. Patient age negatively affected the postoperative graft synovial coverage and chondral status but did not affect the clinical outcomes.

•

Second-look arthroscopy is a direct evaluation of the transplanted graft.

•

There are very few studies of second-look arthroscopy of transplanted PCL grafts.

•

Arthroscopic findings in the PM graft were inferior to those in the AL graft.

•

Poorer synovial coverage in the PM graft was observed in the patients ≥40 years.

Sequential Changes in Posterior Tibial Translation After Posterior Cruciate Ligament Reconstruction: Risk Factors for Residual Posterior Sagging

Background:

Residual posterior sagging may occur after posterior cruciate ligament (PCL) reconstruction (PCLR), yet when it mainly occurs is not fully understood.

Purpose:

To elucidate sequential changes in radiographic posterior tibial translation (PTT) after PCLR.

Study Design:

Case-control study; Level of evidence, 3.

Methods:

The authors retrospectively investigated the radiographic findings from 22 patients who underwent bisocket double-bundle PCLR for isolated PCL injury with at least 2 years of follow-up (mean, 4.5 years; range, 2-10 years). Injury severity was assessed using PTT on lateral radiographs with gravity sag views and was stratified according to side-to-side difference in the tibial-femoral stepoff: grade 1 (<5 mm), grade 2 (5 to <10 mm), or grade 3 (≥10 mm). Measurements were taken preoperatively and then immediately, 3 months, 6 months, 1 year, and ≥2 years postoperatively. The authors also investigated the risk factors for residual posterior sagging, indicated when PTT was ≥5 mm (grade ≥2) at the minimum 2-year follow-up.

Results:

Preoperatively, 13 patients had a grade 2 injury, and 9 had grade 3 injury. The PTT, restored immediately after PCLR, significantly increased at 3 months (P < .001) but remained unchanged thereafter ≥2 years. There were 7 cases of postoperative PTT ≥5 mm on radiographs. Patients with residual posterior sagging had significantly larger mean PTT than did those without residual posterior sagging at all time points except for immediately postoperatively (preoperatively, 9.1 ± 1.6 vs 12.2 ± 2.3 mm; 3-month follow-up, 2.7 ± 1.6 vs 7.0 ± 1.8 mm; ≥2-year follow-up, 3.4 ± 1.0 vs 6.5 ± 1.4 mm; P < .001 for all). Multivariate logistic regression analysis showed that preoperative grade 3 injury was independently associated with residual posterior sagging (OR, 26.809; 95% CI, 1.257-571.963; P < .001).

Conclusion:

The initially reduced postoperative PTT significantly increased within 3 months using conventional rehabilitation protocols, but no progression was observed up to 4.5 years after PCLR. Preoperative grade 3 injury was independently associated with residual posterior sagging.

Evolving evidence in the treatment of primary and recurrent posterior cruciate ligament injuries, part 2: surgical techniques, outcomes and rehabilitation

Isolated and combined posterior cruciate ligament (PCL) injuries are associated with severe limitations in daily, professional, and sports activities as well as with devastating long-term effects for the knee joint. As the number of primary and recurrent PCL injuries increases, so does the body of literature, with high-quality evidence evolving in recent years. However, the debate about the ideal treatment approach such as; operative vs. non-operative; single-bundle vs. double-bundle reconstruction; transtibial vs. tibial inlay technique, continues. Ultimately, the goal in the treatment of PCL injuries is restoring native knee kinematics and preventing residual posterior and combined rotatory knee laxity through an individualized approach. Certain demographic, anatomical, and surgical risk factors for failures in operative treatment have been identified. Failures after PCL reconstruction are increasing, confronting the treating surgeon with challenges including the need for revision PCL reconstruction. Part 2 of the evidence-based update on the management of primary and recurrent PCL injuries will summarize the outcomes of operative and non-operative treatment including indications, surgical techniques, complications, and risk factors for recurrent PCL deficiency. This paper aims to support surgeons in decision-making for the treatment of PCL injuries by systematically evaluating underlying risk factors, thus preventing postoperative complications and recurrent knee laxity. LEVEL OF EVIDENCE: V.

Computational frame of ligament in situ strain in a full knee model

The biomechanical function of connective tissues in a knee joint is to stabilize the kinematics-kinetics of the joint by augmenting its stiffness and limiting excessive coupled motion. The connective tissues are characterized by an in vivo reference configuration (in situ strain) that would significantly contribute to the mechanical response of the knee joint. In this work, a novel iterative method for computing the in situ strain at reference configuration was presented. The framework used an in situ strain gradient approach (deformed reference configuration) and a detailed finite element (FE) model of the knee joint. The effect of the predicted initial configuration on the mechanical response of the joint was then investigated under joint axial compression, passive flexion, and coupled rotations (adduction and internal), and during the stance phase of gait. The inclusion of the reference configuration has a minimal effect on the knee joint mechanics under axial compression, passive flexion, and at two instances (0% and 50%) of the stance phase of gait. However, the presence of the ligaments in situ strains significantly increased the joint stiffness under passive adduction and internal rotations, as well as during the other simulated instances (25%, 75% and 100%) of the stance phase of gait. Also, these parameters substantially altered the local loading state of the ligaments and resulted in better agreement with the literature during joint flexion. Therefore, the proposed computational framework of ligament in situ strain will help to overcome the challenges in considering this crucial biological aspect during knee joint modeling. Besides, the current construct is advantageous for a better understanding of the mechanical behavior of knee ligaments under physiological and pathological states and provide relevant information in the design of reconstructive treatments and artificial grafts.

Thick Graft Versus Double-Bundle Technique on Posterior Cruciate Ligament Reconstruction: Experimental Biomechanical Study with Cadavers

Objective  To evaluate the biomechanical effect of graft thickness compared with the double-bundle technique on posterior cruciate ligament (PCL) reconstruction in human cadaveric knees. Methods  A total of 9 human cadaveric knees were tested in 5 conditions: intact knee (INT); single-bundle reconstruction with a 10-mm quadriceps tendon (SB); double-bundle reconstruction with a 10 mm-quadriceps tendon for the anterolateral bundle and a 7-mm doubled semitendinosus tendon for the posteromedial bundle (DB); single-bundle reconstruction with a 10-mm quadriceps tendon plus a 7-mm doubled semitendinosus tendon (SBT); and PCL-deficient (NoPCL). The posterior tibial translation (PTT) was measured in response to a 134-N posterior tibial load at 0 ^∘ , 30 ^∘ , 60 ^∘ e 90 ^∘ of knee flexion. Results  The PTT values of the DB and SBT techniques were always significantly lower (better stability) than those of the SB technique. The PTT values of the SBT technique were significantly lower than those of the DB technique at 60 ^∘ ( p  = 0.005) and 90 ^∘ ( p  = 0.001). Conclusions  Graft enlargement improves knee stability in isolated PCL reconstructions, whereas the graft division in the two-bundle technique worsens this stability at 60 ^∘ and 90 ^∘ of knee flexion. The findings of the present study suggest that knee stability in PCL reconstructions may be improved with the use of thicker grafts in the SB technique rather than performing the DB technique.

Outcomes After Posterior Cruciate Ligament (PCL) Reconstruction in Patients With Isolated and Combined PCL Tears

Background:

Posterior cruciate ligament (PCL) reconstructions are rarely performed compared with that for the anterior cruciate ligament (ACL).

Purpose:

To evaluate the clinical and functional outcome after isolated or multiligament PCL reconstruction.

Study Design:

Cohort study; Level of evidence, 3.

Methods:

Patients who underwent PCL reconstruction between 2002 and 2010 were included. Standardized follow-up was performed between 2012 and 2013 and consisted of subjective scores (Tegner activity score, Knee injury and Osteoarthritis Outcome Score [KOOS], and subjective International Knee Documentation Committee [IKDC] score) and objective measures, including knee laxity (KT-1000), extension strength, and overall IKDC score.

Results:

One hundred ninety-six patients were identified, of which 172 were available for postoperative follow-up: 39.3% with isolated PCL and 60.7% with multiligament injury. One hundred ten patients were available to complete both clinical follow-up and subjective questionnaires; 62 patients returned the subjective questionnaires. Mean follow-up was 5.9 years (range, 3.1-9.7 years). KOOS scores at follow-up in the isolated PCL group by subscale were 74 (symptoms), 76 (pain), 80 (activities of daily living), 55 (sport), and 55 (quality of life). Scores for patients in the multiligament group were 73 (symptoms), 79 (pain), 82 (activities of daily living), 53 (sport), and 56 (quality of life). Tegner scores were 4.5 and 4.4, respectively, and subjective IKDC scores were 63.8 and 65.0. The mean side-to-side difference in knee laxity was 2.7 mm in the isolated PCL group compared with 2.8 mm in the multiligament group. At 1-year follow-up there were significant differences in KOOS outcome scores between the isolated PCL subgroup and the multiligament subgroup, but no differences at final follow-up. Twelve patients (5%) had PCL revision surgery within the follow-up period.

Conclusion:

Despite the type of injury, there were only minor differences in knee laxity and subjective outcome scores between the isolated PCL group and the multiligament group. The overall revision rate in this study was 5.2%.

Loading Patterns of the Posterior Cruciate Ligament in the Healthy Knee: A Systematic Review

BACKGROUND

The posterior cruciate ligament (PCL) is the strongest ligament of the knee, serving as one of the major passive stabilizers of the tibio-femoral joint. However, despite a number of experimental and modelling approaches to understand the kinematics and kinetics of the ligament, the normal loading conditions of the PCL and its functional bundles are still controversially discussed.

OBJECTIVES

This study aimed to generate science-based evidence for understanding the functional loading of the PCL, including the anterolateral and posteromedial bundles, in the healthy knee joint through systematic review and statistical analysis of the literature.

DATA SOURCES

MEDLINE, EMBASE and CENTRAL.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Databases were searched for articles containing any numerical strain or force data on the healthy PCL and its functional bundles. Studied activities were as follows: passive flexion, flexion under 100N and 134N posterior tibial load, walking, stair ascent and descent, body-weight squatting and forward lunge.

METHOD

Statistical analysis was performed on the reported load data, which was weighted according to the number of knees tested to extract average strain and force trends of the PCL and identify deviations from the norms.

RESULTS

From the 3577 articles retrieved by the initial electronic search, only 66 met all inclusion criteria. The results obtained by aggregating data reported in the eligible studies indicate that the loading patterns of the PCL vary with activity type, knee flexion angle, but importantly also the technique used for assessment. Moreover, different fibres of the PCL exhibit different strain patterns during knee flexion, with higher strain magnitudes reported in the anterolateral bundle. While during passive flexion the posteromedial bundle is either lax or very slightly elongated, it experiences higher strain levels during forward lunge and has a synergetic relationship with the anterolateral bundle. The strain patterns obtained for virtual fibres that connect the origin and insertion of the bundles in a straight line show similar trends to those of the real bundles but with different magnitudes.

CONCLUSION

This review represents what is now the best available understanding of the biomechanics of the PCL, and may help to improve programs for injury prevention, diagnosis methods as well as reconstruction and rehabilitation techniques.

Emerging Updates on the Posterior Cruciate Ligament: A Review of the Current Literature

The posterior cruciate ligament (PCL) is recognized as an essential stabilizer of the knee. However, the complexity of the ligament has generated controversy about its definitive role and the recommended treatment after injury. A proper understanding of the functional role of the PCL is necessary to minimize residual instability, osteoarthritic progression, and failure of additional concomitant ligament graft reconstructions or meniscal repairs after treatment. Recent anatomic and biomechanical studies have elucidated the surgically relevant quantitative anatomy and confirmed the codominant role of the anterolateral and posteromedial bundles of the PCL. Although nonoperative treatment has historically been the initial treatment of choice for isolated PCL injury, possibly biased by the historically poorer objective outcomes postoperatively compared with anterior cruciate ligament reconstructions, surgical intervention has been increasingly used for isolated and combined PCL injuries. Recent studies have more clearly elucidated the biomechanical and clinical effects after PCL tears and resultant treatments. This article presents a thorough review of updates on the clinically relevant anatomy, epidemiology, biomechanical function, diagnosis, and current treatments for the PCL, with an emphasis on the emerging clinical and biomechanical evidence regarding each of the treatment choices for PCL reconstruction surgery. It is recommended that future outcomes studies use PCL stress radiographs to determine objective outcomes and that evidence level 1 and 2 studies be performed to assess outcomes between transtibial and tibial inlay reconstructions and also between single- and double-bundle PCL reconstructions.

Consequences of tibial tunnel reaming on the meniscal roots during cruciate ligament reconstruction in a cadaveric model, Part 2: The posterior cruciate ligament

BACKGROUND

Recent emphasis has turned to reconstructing the posterior cruciate ligament (PCL) after injury. However, single-bundle PCL reconstruction of the anterolateral bundle may potentially injure the posterior meniscal roots.

PURPOSE/HYPOTHESIS

The purpose of this study was to determine if posterior meniscal root injuries occurred because of tunnel reaming for single-bundle PCL reconstruction. It was hypothesized that tibial tunnel reaming within the anterolateral bundle footprint during PCL reconstruction would result in clinically significant decreases in posteromedial (PM) root attachment areas and in ultimate failure strength for the PM root.

STUDY DESIGN

Controlled laboratory study.

METHODS

Testing was performed on 12 matched pairs of human cadaveric knees. For each pair of knees, one knee was left intact, while the contralateral knee was prepared with a tibial tunnel placed 5 mm anterior to the center of the tibial PCL attachment and within the previously described footprint of the anterolateral bundle of the PCL for single-bundle PCL reconstruction. The attachment areas of the posterior meniscal roots were measured with a coordinate measuring device before and after PCL tunnel reaming. The posterior meniscal roots were then pulled to failure with a dynamic tensile testing machine.

RESULTS

There was a significant mean decrease in the attachment area of the PM root (%Δ, 28%; 95% CI, 16-40) after PCL tunnel reaming compared with the intact state (P=.005). The mean ultimate failure strength of the native PM root (mean, 440 N; 95% CI, 347-534) was also significantly stronger (mean, 40%; 95% CI, 18-61; P=.005) than that of the PM root after PCL tunnel reaming (mean, 243 N; 95% CI, 176-309). No changes were found for the posterolateral (PL) root after PCL tunnel reaming.

CONCLUSION

Tibial tunnel reaming for single-bundle PCL reconstruction in the anterolateral bundle footprint significantly reduced the ultimate failure strength and attachment area of the PM meniscal root. The attachment area and ultimate failure strength of the PL root were unaffected by tunnel reaming.

CLINICAL RELEVANCE

Tibial tunnels reamed in the footprint of the anterolateral bundle during single-bundle PCL reconstruction can cause iatrogenic damage to the PM meniscal root attachment. Thus, tibial tunnels should strive to be reamed in the center of the entire tibial PCL attachment site during PCL reconstruction.

Biomechanical analysis of posterior cruciate ligament reconstruction with aperture femoral fixation

The goal of this study was to determine whether single-tunnel-double-bundle-equivalent posterior cruciate ligament (PCL) reconstruction using an aperture femoral fixation device better replicated normal knee kinematics than single-bundle reconstruction. Eight fresh-frozen human cadaver knees underwent arthroscopically assisted PCL reconstruction and were examined with a robotic testing system to assess knee joint kinematics under combinations of applied internal, neutral, and external rotational tibial torque and anteroposterior translational forces at 0°, 30°, 60°, 90°, and 120° flexion. Three conditions were tested: (1) intact PCL; (2) single-tunnel PCL reconstruction with anterolateral and posteromedial bundle fixation at 90°/90° (single bundle); and (3) 90°/0° (double-bundle equivalent), respectively. Posterior tibial translation was the primary outcome measure. Compared with the intact knee, double-bundle-equivalent reconstruction under external tibial torque allowed greater posterior translation across the flexion arc as a whole (P=.025) and at 30° flexion (P=.027) when results were stratified by flexion angle. No other kinematic differences were found with single-bundle or double-bundle-equivalent fixation, including mediolateral translation and both coupled and isolated tibial rotation (P>.05). Single-bundle PCL reconstruction closely approximated native knee rotational and translational kinematics, whereas double-bundle-equivalent reconstruction permitted increased posterior translation with applied external tibial torque, particularly at lower flexion angles. Single-bundle PCL reconstruction provides knee stability similar to the intact condition, making it a practical alternative to conventional double-bundle PCL reconstruction. The authors found that double-bundle-equivalent reconstruction provided no advantage to justify its clinical use.

Posterior cruciate ligament graft fixation angles, part 2: biomechanical evaluation for anatomic double-bundle reconstruction

BACKGROUND

Prior studies have suggested that anatomic double-bundle (DB) posterior cruciate ligament reconstruction (PCLR) reduces residual laxity compared with the intact state better than single-bundle PCLR. Although the anterolateral bundle (ALB) and posteromedial bundle (PMB) reportedly act codominantly, few studies have compared commonly used graft fixation angles and the influence that graft fixation angles have on overall graft forces and knee laxity.

HYPOTHESIS

Graft fixation angle combinations of 0°/75° (PMB/ALB), 0°/90°, 0°/105°, 15°/75°, 15°/90°, and 15°/105° would significantly reduce knee laxity from the sectioned PCL state while preventing in vitro graft forces from being overloaded between any of the graft fixation angles.

STUDY DESIGN

Controlled laboratory study.

METHODS

Nine cadaveric knees were evaluated for the kinematics of the intact, PCL-sectioned, and DB PCLR techniques. The DB technique was varied by fixing the PMB and ALB grafts at the following 6 randomly ordered fixation angle combinations: 0°/75° (PMB/ALB), 0°/90°, 0°/105°, 15°/75°, 15°/90°, and 15°/105°. A 6 degrees of freedom robotic testing system subjected each specimen to an applied 134-N posterior tibial load at 0° to 120° of flexion and 5-N·m external, 5-N·m internal, and 10-N·m valgus rotation torques applied at 60°, 75°, 90°, 105°, and 120° of flexion. The ALB and PMB grafts were fixed to load cells that concurrently measured graft forces throughout kinematic testing. t tests compared the kinematics between groups, and 2-factor models assessed the contribution of ALB and PMB grafts after DB PCLR (P < .05).

RESULTS

Consistently, DB PCLR significantly reduced posterior translation compared with the sectioned PCL and was comparable with the intact state during applied posterior tibial loads at flexion angles of greater than 90°; a mean residual laxity of 1.5 mm remained compared with the intact state during applied posterior tibial loads. Additionally, fixing the PMB graft at 15° resulted in significantly larger PMB graft forces compared with fixation at 0° during applied posterior loading, internal rotation, external rotation, and valgus rotation. Similarly, fixing the ALB graft at 75° resulted in significantly larger ALB graft forces compared with fixation of the ALB graft at 90° or 105° during all loading conditions.

CONCLUSION

Fixation of the PMB graft at 0° to 15° and the ALB graft at 75° to 105° during DB PCLR were successful in significantly reducing knee laxity from the sectioned state. However, fixation of the PMB graft at 15° versus 0° resulted in significantly increased loads through the PMB graft, and fixation of the ALB graft at 75° versus 90° or 105° resulted in significantly increased loads through the ALB graft.

CLINICAL RELEVANCE

This study found that all 6 fixation angle combinations significantly improved knee kinematics compared with the sectioned state at time zero; however, it is recommended that fixation of the PMB graft be performed at 0° because of the significant increases in PMB graft loading that occur with fixation at 15° and that fixation of the ALB graft be performed at 90° or 105° rather than 75° to minimize ALB graft forces, which could lead to graft attenuation or failure over time.

Posterior cruciate ligament graft fixation angles, part 1: biomechanical evaluation for anatomic single-bundle reconstruction

BACKGROUND

Currently, no consensus exists for the optimal graft fixation angle for anatomic single-bundle (SB) posterior cruciate ligament reconstructions (PCLRs). Additionally, direct graft forces have not been measured. Alternative graft fixation angles and the resultant graft forces should be investigated to optimize the stability of SB PCLRs without overconstraining the knee.

HYPOTHESIS

Graft fixation angles of 75°, 90°, and 105° for SB PCLR were hypothesized to improve knee stability compared with the sectioned posterior cruciate ligament state with no evidence of knee overconstraint.

STUDY DESIGN

Controlled laboratory study.

METHODS

Nine fresh-frozen human cadaveric knees were biomechanically evaluated for the intact, sectioned, and SB PCLR states with the anterolateral bundle graft fixed at 75°, 90°, and 105°. A 6 degrees of freedom robotic system assessed knee laxity with a 134-N posterior load applied at 0° to 120° and 5-N·m external, 5-N·m internal, and 10-N·m valgus rotation torques applied at 60° to 120°. By securing the graft to an external load cell, graft forces were measured throughout kinematic testing.

RESULTS

No significant kinematic differences were found among the 3 fixation angles. Each fixation angle resulted in significantly less posterior translation than in the sectioned state at all flexion angles (P < .05), with 4.1 mm of average residual laxity during an applied posterior loading. For all graft fixation angles, internal rotation was significantly increased between 60° and 120° of flexion, and external rotation was significantly increased at 90°, 105°, and 120° of flexion compared with the intact state. Graft forces were not significantly different among the 3 fixation angles and remained below reported loads observed during activities of daily living.

CONCLUSION

All tested SB PCLR graft fixation angles restored knee laxity to similar levels; however, persistent laxity resulted in significant increases in knee laxity compared with the intact state during posterior tibial loading at all flexion angles, internal rotation at flexion angles ≥60°, and external rotation at ≥75° of flexion.

CLINICAL RELEVANCE

The results of this study suggest that SB PCL graft fixation angles of 75°, 90°, and 105° were comparable in restoring knee kinematics and exposed the graft to similar time-zero loads. However, SB PCLRs did not fully reduce knee laxity to the intact state.

A review of the anatomical, biomechanical and kinematic findings of posterior cruciate ligament injury with respect to non-operative management

An understanding of the kinematics of posterior cruciate ligament (PCL) deficiency is important for the diagnosis and management of patients with isolated PCL injury. The kinematics of PCL injury has been analysed through cadaveric and in vivo imaging studies. Cadaveric studies have detailed the anatomy of the PCL. It consists of two functional bundles, anterolateral and posteromedial, which exhibit different tensioning patterns through the arc of knee flexion. Isolated sectioning of the PCL and its related structures in cadaveric specimens has defined its primary and secondary restraining functions. The PCL is the primary restraint to posterior tibia translation above 30° and is a secondary restraint below 30° of knee flexion. Furthermore, sectioning of the PCL produces increased chondral deformation forces in the medial compartment as the knee flexes. However, the drawback of cadaveric studies is that they can not replicate the contribution of surrounding neuromuscular structures to joint stability that occurs in the clinical setting. To address this, there have been in vivo studies that have examined the kinematics of the PCL deficient knee using imaging modalities whilst subjects perform dynamic manoeuvres. These studies demonstrate significant posterior subluxation of the medial tibia as the knee flexes. The results of these experimental studies are in line with clinical consequences of PCL deficiency. In particular, arthroscopic evaluation of subjects with isolated PCL injuries demonstrate an increased incidence of chondral lesions in the medial compartment. Yet despite the altered kinematics with PCL injury only a minority of patients require surgery for persistent instability and the majority of athletes are able to return to sport following a period of non-operative rehabilitation. Specifically, non-operative management centres on a programme of quadriceps strengthening and hamstring inhibition to minimise posterior tibial load. The mechanism behind the neuromuscular adaptation that allows the majority of athletes to return to sport has been investigated but not clearly elucidated. The purpose of this review paper is to draw together the findings of experimental studies on the anatomical and kinematic effects of PCL injury and summarise their relevance with respect to non-operative management and functional outcome in patients with isolated PCL deficiency.

Functional outcome following PCL and complex knee ligament reconstruction

The purpose of this study was to evaluate the functional outcome of surgical reconstruction of the posterior cruciate ligament (PCL). In particular we wanted to document the recovery of knee muscle function. Twenty three patients underwent single bundle reconstruction of the PCL. There were four isolated PCL reconstructions. The remainder had PCL reconstructions combined with other ligament reconstructions. Patients were followed up at 2, 6, 12 and 26 weeks post operatively and underwent detailed functional assessment at 12 and 24 months. Outcome measures included the International Knee Documentation Committee (IKDC) score, the Tegner activity rating, and muscle dynamometry evaluating peak torque for knee flexion and extension. At final follow up 19 (83%) patients were rated as normal or nearly normal by the IKDC score. Seventeen (74%) patients returned to moderate or strenuous activity. Ligament stability was rated as normal or nearly normal in 20 (87%) patients. All 23 patients regained normal or nearly normal range of motion of the knee following surgery. Knee flexion peak torque demonstrated an average percentage deficit from the normal side of 24% at 12 months and 14% at 24 months. The deficits for extension were 35% and 9% for the same time points. PCL reconstruction is associated with a satisfactory clinical outcome but muscle function abnormalities may persist for 2 years.

Application of Raman scattering to the measurement of ligament tension

More marginal results and complications occur as a result of knee ligament surgery than of other common surgical procedure. Long-term success rates of anterior cruciate ligament reconstruction range between 75 and 90%. The goal of knee surgery is to restore the normal kinematics of the knee. If the tension is too high, the range of motion of the joint is restricted, resulting in abnormal stresses on the articular cartilage and the meniscuses, and interfering with the revascularization of the graft. The use of Raman spectroscopy for the measurement of tension in ligaments and tendons is described. Measurements of the Raman spectrum demonstrate that the Raman frequencies shift with applied tension.

The biomechanical performance of bone block and soft-tissue posterior cruciate ligament graft fixation with interference screw and cross-pin techniques

PURPOSE

The purpose of this study was to evaluate the biomechanical properties of 4 different graft fixation constructs on the tibial side of the posterior cruciate ligament with reconstruction by use of an Achilles tendon graft.

METHODS

Biomechanical testing of 4 different fixation techniques was performed on 20 human cadaveric tibias and Achilles tendons. Cross-pin fixation with bone blocks (group A), interference screw fixation with bone blocks (group B), cross-pin fixation of soft tissue with backup fixation (group C), and interference screw fixation of soft tissue with backup fixation (group D) were tested. The tibia-graft fixation complex was cyclically loaded between 50 N and 250 N at 1 Hz for 1,000 cycles. After cycling, the amount of graft displacement was determined by measuring the change in grip-to-grip distance. The complex was then loaded to failure at 1 mm/s, and maximum failure load, stiffness, and mode of failure were determined.

RESULTS

Group C had a higher maximum failure load and stiffness than groups A and B (P < .05 and P < .001, respectively) but poor results for displacement (P < .05 and P < .05, respectively). The failure modes were bone block fracture, graft laceration, or cross-pin fracture in the cross-pin groups and graft pullout in the interference screw groups.

CONCLUSIONS

Our study suggests that maximum failure load and stiffness of hybrid fixation for Achilles tendon graft are comparable to those of both single calcaneal bone plug fixation methods that we studied. However, tendon graft displacement was significantly greater regardless of fixation method when compared with bone plug fixation.

CLINICAL RELEVANCE

Hybrid fixation for soft-tissue graft on the tibial fixation site provides comparable biomechanical properties of bone-to-bone fixation.

Effect of posterior cruciate ligament deficiency on in vivo translation and rotation of the knee during weightbearing flexion

BACKGROUND

The effect of posterior cruciate ligament (PCL) deficiency on 6 degrees of freedom in vivo knee-joint kinematics is unclear.

HYPOTHESIS

In addition to constraining anterior-posterior translation, the PCL also functions to constrain the medial-lateral translation and rotation of the knee during weightbearing flexion of the knee.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eight patients with a PCL injury in 1 knee and the other intact were scanned with magnetic resonance imaging, and 3-dimensional models of the femur and tibia were created for both knees. Each knee was imaged during quasistatic weight-bearing flexion (from 0 degrees to 105 degrees ) using a dual-orthogonal fluoroscopic system. The translation and rotation of the PCL-deficient knee were compared with the intact contralateral control.

RESULTS

Posterior cruciate ligament deficiency caused an increase in posterior tibial translation beyond 30 degrees of flexion compared with the intact contralateral knees. At 90 degrees of flexion, PCL deficiency increased posterior tibial translation by 3.5 mm (P < .05). In the medial-lateral direction, PCL deficiency resulted in a 1.1 mm increase in lateral tibial translation at 90 degrees of flexion (P < .05). With regard to rotation, PCL deficiency caused a significantly lower varus rotation (on average, 0.6 degrees lower) at 90 degrees of flexion. Posterior cruciate ligament deficiency caused a decreased internal tibial rotation throughout the range of flexion, but no significant difference was detected.

CONCLUSIONS

This study quantitatively describes the effect of PCL injury on 6 degrees of freedom kinematics of the knee during quasistatic weightbearing flexion. Using the intact contralateral side as a control, we found that PCL injuries not only affect anterior-posterior tibial translation but also medial-lateral translation and rotation of the knee.

CLINICAL RELEVANCE

These data provide baseline knowledge of the in vivo kinematics of the knee after PCL injury. Surgical reconstruction of the injured PCL, either using single-bundle or double-bundle technique, should not only focus on restoration of posterior stability of the knee but also the medial-lateral stability as well as the rotational stability. These findings may help to explain the long-term degenerative changes seen in PCL-deficient knees.

Effect of tibial positioning on the diagnosis of posterolateral rotatory instability in the posterior cruciate ligament-deficient knee

OBJECTIVE

To determine whether positioning of the tibia affects the degree of tibial external rotation seen during a dial test in the posterior cruciate ligament (PCL)-posterolateral corner (PLC)-deficient knee.

DESIGN

Laboratory investigation.

SETTING

Biomechanics laboratory.

HYPOTHESIS

An anterior force applied to the tibia in the combined PCL-PLC-deficient knee will yield increased tibial external rotation during a dial test.

METHODS

The degree of tibial external rotation was measured with 5 Nm of external rotation torque applied to the tibia at both 30 degrees and 90 degrees of knee flexion. Before the torque was applied, an anterior force, a posterior force, or neutral (normal, reduced control) force was applied to the tibia. External rotation measurements were repeated after sequential sectioning of the PCL, the posterolateral structures and the fibular collateral ligament (FCL).

RESULTS

Baseline testing of the intact specimens demonstrated a mean external rotation of 18.6 degrees with the knee flexed to 30 degrees (range 16.1-21.0 degrees ), and a mean external rotation of 17.3 degrees with the knee flexed to 90 degrees (range 13.8-20.0 degrees ). Sequential sectioning of the PCL, popliteus and popliteofibular ligament, and the FCL led to a significant increase in tibial external rotation compared with the intact knee for all testing scenarios. After sectioning of the popliteus and popliteofibular ligament, the application of an anterior force during testing led to a mean tibial external rotation that was 5 degrees greater than during testing in the neutral position and 7.5 degrees greater than during testing with a posterior force. In the PCL, popliteus/popliteofibular ligament and FCL-deficient knee, external rotation was 9 degrees and 12 degrees greater with the application of an anterior force during testing compared with neutral positioning and the application of a posterior force, respectively.

CONCLUSION

An anterior force applied to the tibia during the dial test in a combined PCL-PLC-injured knee increased the overall amount of observed tibial external rotation during the dial test. The anterior force reduced the posterior tibial subluxation associated with PCL injury, which is analogous to what is observed when the dial test is performed with the patient in the prone position. Reducing the tibia with either an anterior force when the patient is supine or performing the dial test with the patient in the prone position increases the ability of an examiner to detect a concomitant PLC injury in the setting of a PCL-deficient knee.

Evaluation of in situ graft forces of a 2-bundle tibial inlay posterior cruciate ligament reconstruction at various flexion angles

PURPOSE

The purpose of this study is to evaluate a posterior cruciate ligament (PCL) reconstruction using a 2-bundle (anterolateral [AL] and posteromedial [PM]) posterior tibial inlay reconstructive technique fixed at various degrees of flexion.

METHODS

Eight human cadaveric knee specimens underwent a 2-bundle/posterior inlay PCL reconstruction. A testing apparatus was developed with force gauges placed on the AL and PM bundles, respectively. The PCL 2-bundle complex was pretensioned and placed through an arc of motion from 0 degrees to 105 degrees with measurement obtained at 15 degrees increments. Testing conditions included 3 different tension parameters of the AL and PM bundles: (1) AL and PM bundles both at 90 degrees, (2) AL and PM bundles both at 45 degrees, and (3) differential tensioning the AL bundle at 90 degrees and the PM bundle at 0 degrees.

RESULTS

The results revealed that tensioning of the AL bundle at 90 degrees and PM bundle at 0 degrees produced reciprocal in situ forces similar to the native PCL. Through a complete knee arc of motion, at least 1 of the 2 bundles maintained tension in a reciprocal fashion. Data from the other reconstructive conditions revealed there was significant and excessive in situ loads above the pretensioned loads transmitted through the PM bundle with increased extension.

CONCLUSIONS

This in vitro PCL reconstructive study using an anatomic tibal inlay and 2-bundle (AL and PM) approach with the AL bundle fixed at 90 degrees and the PM bundle at 0 degrees flexion produces a symmetrical reciprocal force pattern with 1 limb of the graft under continuous tension throughout a full arc of motion, whereas the other 2 testing conditions (AL/PM at 45/45 and 90/90) produce excessive force in the PM bundle with lower degrees of flexion.

CLINICAL RELEVANCE

This cadaver study showed the PCL technique using 2-bundle/tibial inlay technique and fixation of the AL bundle at 90 degrees of flexion and the PM bundle at 0 degrees flexion reproduced anatomic in situ graft forces in a reciprocal pattern.

Kinematics of the posterior cruciate ligament/posterolateral corner-injured knee after reconstruction by single- and double-bundle intra-articular grafts

BACKGROUND

Single- and double-bundle reconstructions have been proposed for the knee after combined posterior cruciate ligament/posterolateral corner injuries.

HYPOTHESIS

The double-bundle posterior cruciate ligament reconstruction is superior to the single-bundle posterior cruciate ligament reconstruction with regard to restoration of normal knee kinematics to the posterior cruciate ligament/posterolateral corner-sectioned knee.

STUDY DESIGN

Controlled laboratory study.

METHODS

Kinematics of 8 fresh-frozen, cadaveric human knees were determined in the following conditions: intact, sectioned posterior cruciate ligament/posterolateral corner, single anterolateral bundle posterior cruciate reconstruction, and double-bundle posterior cruciate reconstruction.

RESULTS

The sectioned knee demonstrated a posterior shift of the tibial neutral position and the abnormal posterior, varus, and external rotation laxities used clinically to define a combined posterior cruciate ligament/posterolateral corner injury. Both reconstructions restored the posterior laxity to levels that were not statistically different from those seen in the intact knee, but the double-bundle reconstruction more closely mimicked the posterior laxity profile of the intact knee, having statistically lower posterior laxities than did the single-bundle reconstruction at 30 degrees, 60 degrees, and 90 degrees of flexion (P < .05, analysis of variance, HSD test). The resting position of the tibia after double-bundle reconstruction trended to be anteriorly subluxated relative to its position for the intact knee at flexion angles of 30 degrees and greater (P <.05, paired t test). Neither technique corrected the abnormal varus or external rotation laxities.

CONCLUSION

With either single- or double-bundle reconstructions, additional posterolateral reconstruction is recommended to correct the external rotation laxity.

CLINICAL RELEVANCE

Knowledge of the kinematics of the combined posterior cruciate ligament/posterolateral corner-injured knee is important in the proper diagnosis of the injury and in the selection of the appropriate surgical reconstruction.

Importance of femoral tunnel placement in double-bundle posterior cruciate ligament reconstruction: biomechanical analysis using a robotic/universal force-moment sensor testing system

BACKGROUND

Previous studies have identified the femoral attachment of the posterior cruciate ligament fibers as one of the primary determinants of fiber tension behavior. In addition, a double-bundle posterior cruciate ligament reconstruction has been shown to restore the intact knee kinematics more closely than does a single-bundle reconstruction.

HYPOTHESIS

An anterior tunnel position in double-bundle posterior cruciate ligament reconstruction restores the biomechanics of the normal knee more closely than does a posterior tunnel position.

STUDY DESIGN

Controlled laboratory study.

METHODS

Kinematics and in situ forces of human knees after double-bundle posterior cruciate ligament reconstruction with 2 different femoral tunnel positions (anterior vs posterior) were evaluated using a robotic/universal force-moment sensor testing system. Within the same specimen, the resulting knee kinematics and in situ forces were compared. For statistical analysis, 2-way analysis of variance repeated measures were performed.

RESULTS

The femoral tunnel position of the double-bundle hamstring graft had significant effect on the resulting posterior tibial displacement and in situ forces of the hamstring grafts. The anterior femoral tunnel position provided significantly less posterior tibial translation than did the posterior tunnel position. There was a tendency toward higher in situ forces of grafts fixed in the anterior tunnel when compared to the posterior position, but this difference was statistically not significant.

CONCLUSION

An anterior position of the bone tunnels in double-bundle posterior cruciate ligament reconstruction restores the normal knee kinematics more closely than does a posterior position of the tunnels.

CLINICAL RELEVANCE

In double-bundle posterior cruciate ligament reconstruction, posterior placement of the tunnel should be avoided.

Biomechanics of initial tibial fixation in posterior cruciate ligament reconstruction

PURPOSE

Clinical success of posterior cruciate ligament (PCL) reconstruction continues to lag behind that of its anterior counterpart. The tibial site of PCL graft fixation has been a focus of recent research. This study examined the effect of combined distal and proximal tibial fixation on the ability of a transtibial PCL reconstruction to restore intact knee kinematics and in situ forces of the intact PCL.

TYPE OF STUDY

Biomechanical study.

METHODS

Ten human cadaveric knees were tested. A 134-N posterior tibial load was applied using a robotic/universal force moment sensor testing system at 0 degrees, 30 degrees, 60 degrees, 90 degrees, and 120 degrees of knee flexion. Each knee was tested under 4 conditions: intact, PCL-deficient, single-bundle transtibial reconstruction with distal tibial fixation, and single-bundle transtibial reconstruction with combined distal and proximal tibial fixation. Knee kinematics in 5 degrees of freedom for each condition were recorded and in situ forces of the intact PCL and the PCL grafts were determined.

RESULTS

Reconstruction with combined fixation resulted in significantly less posterior tibial translation than reconstruction with distal fixation at 30 degrees, 90 degrees, and 120 degrees (P < .05), and restored intact knee kinematics at 90 degrees and 120 degrees (P > .05). Reconstruction with combined fixation more closely restored intact PCL in situ forces at 90 degrees (P < .05).

CONCLUSIONS

Transtibial reconstruction with combined fixation more closely restores intact knee kinematics and in situ forces in the PCL at initial fixation than does reconstruction with distal tibial fixation. The improved kinematics and in situ forces seen with the combined fixation may be attributed to decreased functional graft length and increased stiffness of the PCL graft.

CLINICAL RELEVANCE

Combined tibial fixation may provide a more stable reconstruction at initial fixation.

Clinical outcomes after isolated arthroscopic single-bundle posterior cruciate ligament reconstruction

PURPOSE

The purpose of this study was to evaluate the clinical outcomes after arthroscopic single-bundle posterior cruciate ligament (PCL) reconstruction in patients with isolated grade III PCL injuries.

TYPE OF STUDY

Retrospective review.

METHODS

Twenty-one patients who underwent an isolated arthroscopic single-bundle PCL reconstruction for the treatment of a grade III PCL injury between 1989 and 1998 were included in the study. There were 15 male and 6 female patients with an average age of 38 years (range, 20 to 62 years). The length of follow-up was 5.9 years (range, 2.6 to 11 years), and the average time from injury to surgery was 4.5 years (median, 1.3 years; range, 2 weeks to 25 years). All patients completed a subjective evaluation and 14 patients returned for a physical examination and radiographs. One patient underwent an acute reconstruction (<3 weeks), 4 had a subacute (<3 months), and 16 underwent a chronic (>3 months) reconstruction. The anterolateral bundle of the PCL was reconstructed using an Achilles tendon allograft passed through femoral and tibial bone tunnels.

RESULTS

The overall average Activities of Daily Living Scale (ADLS), Sports Activities Scale (SAS), and SF-36 scores were 79.3, 71.6, and 98 points, respectively. There was a significant difference identified when the ADLS (91.3 v 75.6) and the SAS (90.4 v 65.8) scores of the subacute/acute group were compared with those of the chronic reconstruction group. Using the International Knee Documentation Committee (IKDC) subjective assessment, 57% of the patients had normal/near normal knee function, and 62% had a normal/near normal activity level. The average extension and flexion losses were 1 degrees and 5 degrees , respectively. Instrumented laxity examination revealed that 62% had less than a 3-mm and 31% had a 3- to 5-mm side-to-side difference in corrected posterior displacement. Radiographs at follow-up showed that 75% had normal/near normal findings according to IKDC guidelines.

CONCLUSIONS

The clinical outcomes after arthroscopic single-bundle PCL reconstruction in this study produced a satisfactory return of function and improvement in symptoms. All patients in this study had improved laxity of at least 1 grade. When compared with chronic reconstructions, acute reconstructions had statistically significant better ADLS and SAS scores.

LEVEL OF EVIDENCE

IV, case series.

The anatomic characteristics of the tibial insertion of the posterior cruciate ligament

PURPOSE

The purpose of the study was to better define the tibial insertion of the posterior cruciate ligament (PCL) and to identify landmarks that could be used to aid in placement of independent tibial tunnels for a 2-bundle PCL reconstruction.

TYPE OF STUDY

Descriptive anatomic study.

METHODS

Ten knees from 8 cadavers were dissected and the PCL was identified. The ligament was peeled away from its insertion and the sides of the insertion site were measured and recorded. The 4 corners of the insertion site were identified and marked. Observations were made of the morphology of the insertion site and the presence of any reproducible anatomic landmarks. A note was made of landmarks that could be easily identified on all of the specimens by direct vision and by palpation with a probe.

RESULTS

The ligament consisted of 2 regions, 1 anterolateral, and 1 posteromedial, with a gradual change in the laxity of the ligament as the knee was passed through flexion and extension. The insertion site was situated in a depression between the plateaus of the tibia and extended below the articular surface. The average length +/- standard deviation of the 4 sides was 128 +/- 21.2 mm (medial side), 107 +/- 26.5 mm (superior side), 160 +/- 30.0 mm (lateral side), and 169 +/- 34.5 mm (inferior side). The shape and sides of the insertion site were visually similar among the 10 specimens. The superolateral and superomedial corners were both represented by depressions and a reproducible ridge represented the inferior border. These structures could be visualized as well as palpated on all specimens.

CONCLUSIONS

Based on the findings of this study, we describe the anatomic characteristics of the tibial footprint of the PCL. Anatomic reference points that represent the corners of the tibial insertion of the PCL were identified by direct vision or palpation consistently on all specimens included in the study. These reference points could potentially aid in the placement of an anterolateral and posteromedial tibial tunnel for a 2 tibial tunnel PCL reconstruction.

CLINICAL RELEVANCE

Reproducible anatomic reference points exist at the tibial insertion of the PCL that can be identified by direct vision and palpation. These reference points may potentially aid in the placement of separate tibial tunnels for a 2-bundle PCL reconstruction.

A biomechanical comparison of posterior cruciate ligament reconstructions using single- and double-bundle tibial inlay techniques

BACKGROUND

The efficacy of using a double-bundle versus single-bundle graft for posterior cruciate ligament reconstruction has not been demonstrated.

HYPOTHESIS

A double-bundle graft restores knee kinematics better than a single-bundle graft does in tibial inlay PCL reconstructions.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eight cadaveric knees were subjected to 6 cycles from a 40-N anterior reference point to a 100-N posterior translational force at 10 degrees , 30 degrees , 60 degrees , and 90 degrees of flexion. Testing was performed for the intact and posterior cruciate deficient knee as well as for both reconstructed conditions. Achilles tendons, divided into 2 equal sections, were prepared as both single-bundle and double-bundle grafts. Both grafts were employed in the same knee, and the order of graft reconstruction was randomized.

RESULTS

There were no statistical differences in translation between the intact state and either of the reconstructions (P > .05) or between either of the reconstructions at any flexion angle (P > .05).

CONCLUSION

No differences in translation between the 2 graft options were identified.

CLINICAL RELEVANCE

The use of a double-bundle graft may not offer any advantages over a single-bundle graft for tibial inlay posterior cruciate reconstructions.

Cruciate coupling and screw-home mechanism in passive knee joint during extension–flexion

The screw-home mechanism and coupling between forces in cruciate ligaments during passive knee joint flexion were investigated for various boundary conditions, flexion axis alignments and posterior cruciate ligaments (PCL)/anterior cruciate ligament (ACL) conditions. A developed non-linear 3D finite element model was used to perform detailed elasto-static response analyses of the human tibiofemoral joint as a function of flexion angle varying from 10 degrees hyper-extension to 90 degrees flexion. The tibia rotated internally as the femur flexed and externally as the femur extended. The re-alignment of the flexion axis by +/-5 degrees rotation about the axial (distal-proximal) axis, transection of the ACL and changes in cruciate ligament initial strains substantially influenced the 'screw-home' motion. On the other hand, restraint on this coupled rotation diminished ACL forces in flexion. A remarkable coupling was predicted between ACL and PCL forces in flexion; forces in both cruciate ligaments increased as the initial strain or pretension in one of them increased whereas they both diminished as one of them was cut or became slack. This has important consequences in joint functional biomechanics following a ligament injury or replacement surgery and, hence, in the proper management of joint disorders.

Biomechanical analysis of a combined double-bundle posterior cruciate ligament and posterolateral corner reconstruction

BACKGROUND

Failure to address both components of a combined posterior cruciate ligament and posterolateral corner injury has been implicated as a reason for abnormal biomechanics and inferior clinical results.

HYPOTHESIS

Combined double-bundle posterior cruciate ligament and posterolateral corner reconstruction restores the kinematics and in situ forces of the intact knee ligaments.

STUDY DESIGN

Controlled laboratory study.

METHODS

Ten fresh-frozen human cadaveric knees were tested using a robotic testing system through sequential cutting and reconstructing of the posterior cruciate ligament and posterolateral corner. The knees were subjected to a 134-N posterior tibial load and a 5-N.m external tibial torque at multiple flexion angles. The double-bundle posterior cruciate ligament reconstruction was performed using Achilles and semitendinosus tendons. The posterolateral corner reconstruction consisted of reattaching the popliteus tendon to its femoral origin and reconstructing the popliteofibular ligament with a gracilis tendon.

RESULTS

Under the posterior load, the combined reconstruction reduced posterior translation to within 1.2 +/- 1.5 mm of the intact knee. The in situ forces in the posterior cruciate ligament grafts were significantly less than those in the native posterior cruciate ligament at all angles except full extension. Conversely, the forces in the posterolateral corner grafts were significantly higher than those in the native structures at all angles. Under the external torque with the combined reconstruction, external rotation as well as in situ forces in the posterior cruciate ligament and posterolateral corner grafts were not different from the intact knee.

CONCLUSIONS

A combined posterior cruciate ligament and posterolateral corner reconstruction can restore intact knee kinematics at time zero. In situ forces in the intact posterior cruciate ligament and posterolateral corner were not reproduced by the reconstruction; however, the posterolateral corner reconstruction reduced the loads experienced by the posterior cruciate ligament grafts.

CLINICAL RELEVANCE

By addressing both structures of this combined injury, this technique restores native kinematics under the applied loads at fixed flexion angles and demonstrates load sharing among the grafts creating a potentially protective effect against early failure of the posterior cruciate ligament grafts but with increased force in the posterolateral corner construct.

In vivo function of the posterior cruciate ligament during weightbearing knee flexion

BACKGROUND

Current knowledge of posterior cruciate ligament function is mainly based on in vitro cadaveric studies. There are few studies on the in vivo function of the posterior cruciate ligament. The objective of the study was to quantify the multidimensional deformation of the posterior cruciate ligament.

HYPOTHESIS

During in vivo weightbearing flexion, the posterior cruciate ligament undergoes complex 3-dimensional deformations, including elongation, twist, and changes in orientation.

STUDY DESIGN

In vivo biomechanical study.

METHODS

Magnetic resonance images of 5 human knees were used to create 3-dimensional computer models of each subject's knee, including the insertion areas of the posterior cruciate ligament. Orthogonal fluoroscopic images of each subject's knee were acquired as a quasi-static lunge was performed. The images and computer models were used to reproduce the in vivo motion of the knee. The relative motion of the femoral and tibial insertions was described in terms of elongation, twist, elevation (the angle between the tibial plateau and posterior cruciate ligament, measured in the sagittal plane), and deviation (mediolateral orientation, measured in plane of tibial plateau).

RESULTS

The length of the posterior cruciate ligament increased significantly with increasing flexion. It twisted almost 80 degrees as the knee flexed from 0 degrees to 90 degrees . The elevation angle remained relatively constant at 50 degrees . The deviation angle was medially oriented by 20 degrees at full extension, then decreased to approximately 10 degrees at 30 degrees through 90 degrees of flexion.

CONCLUSION

The posterior cruciate ligament undergoes a complex twisting motion as it elongates with flexion.

CLINICAL RELEVANCE

During reconstruction, the tunnels and graft may need to be placed such that the multidimensional deformation of the intact posterior cruciate ligament is reproduced.

Soft-tissue graft fixation in posterior cruciate ligament reconstruction: evaluation of the effect of tibial insertion site on joint kinematics and in situ forces using a robotic/UFS testing system

INTRODUCTION

Surgical reconstruction of the posterior cruciate ligament (PCL) is recommended in acute injuries that result in severe tibial subluxation and instability. The surgical outcome level may be affected by the tibial fixation site. In response to a 110-N posterior tibial load, kinematics and in situ forces of anatomical soft-tissue graft fixation in single-bundle PCL reconstruction using an interference screw fixation are significantly closer to those in the intact knee than with extracortical fixation with two staples.

MATERIALS AND METHODS

Using a robotic/universal force moment sensor (UFS) testing system, we examined joint kinematics and in situ forces of porcine knees following single-bundle PCL reconstruction fixed at two different tibial fixation sites: anatomical interference screw and extracortical fixation.

RESULTS

The site of the tibial graft fixation had significant effect on the resulting posterior displacement and in situ forces of the graft. Both PCL reconstruction techniques reduced the posterior tibial translation significantly. Proximal fixation techniques provided significantly less posterior tibial translation than extracortical fixation. Single-bundle PCL reconstruction with an interference screw showed higher in situ forces of the graft than the extracortical fixation.

CONCLUSIONS

The kinematics and in situ forces of a single-bundle PCL reconstruction using an interference screw fixation technique are superior to the primary stability of an extracortical fixation with staples.

Evaluation and treatment of posterior cruciate ligament injuries: revisited

Current knowledge and treatment of posterior cruciate ligament injuries continue to lag behind that of anterior cruciate ligament injuries. This is the result of the relative infrequency of posterior cruciate ligament injuries and the lack of consensus with respect to its natural history, surgical indications, technique, and postoperative rehabilitation. Recent anatomical and biomechanical studies have improved our understanding of the posterior cruciate ligament in an attempt to reproduce its anatomy and function during reconstruction. The following is a comprehensive review on the evaluation and treatment of posterior cruciate ligament injuries with special focus on the current surgical techniques.

The effect of length on the structural properties of an Achilles tendon graft as used in posterior cruciate ligament reconstruction

BACKGROUND

The clinical outcomes of posterior cruciate ligament reconstruction are varied. No previous studies have investigated the effect of graft length on the structural properties of the graft.

HYPOTHESIS

Graft length significantly affects the structural properties of posterior cruciate ligament grafts.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eight Achilles tendon grafts were tested under tensile loads up to 400 N at 3 different lengths: long (75 mm), medium (48 mm), and short (34 mm). These 3 lengths represent midtunnel fixation, inlay fixation, and fixation near the ligament insertions.

RESULTS

Shortening the graft from both long to medium and from medium to short increased the stiffness by approximately 25%. Long and medium grafts displaced significantly more than medium and short grafts, respectively.

CONCLUSION

The effective length of a graft, which is determined by where it is fixed, should be considered an important variable in posterior cruciate ligament reconstruction.

Biomechanical comparison of tibial inlay versus transtibial techniques for posterior cruciate ligament reconstruction: analysis of knee kinematics and graft in situ forces

BACKGROUND

The tibial inlay technique for posterior cruciate ligament reconstruction has been proposed to provide a more anatomic reconstruction because it eliminates the sharp turn in the graft as it exits the proximal margin of the tibial tunnel in the transtibial technique.

HYPOTHESIS

Reconstruction of the posterior cruciate ligament using the tibial inlay technique would more closely restore intact knee kinematics and in situ forces in the posterior cruciate ligament than would reconstruction using the transtibial technique.

METHODS

Ten human cadaveric knees were tested in a controlled laboratory study. A robotic/universal force-moment sensor testing system was used to apply a 134-N posterior tibial load at 5 knee flexion angles: 0 masculine, 30 masculine, 60 masculine, 90 masculine, and 120 masculine. Four knee conditions were tested: intact, posterior cruciate ligament-deficient, and the single-bundle tibial inlay reconstruction and transtibial posterior cruciate ligament reconstruction.

RESULTS

Both reconstruction techniques restored posterior tibial translations to 1.7 to 2.1 mm of the intact knee, with no statistical differences between the techniques. In response to the posterior tibial load, in situ forces in both grafts were between 7 and 39 N less than those in the intact posterior cruciate ligament, with no significant differences between the grafts.

CLINICAL RELEVANCE

The study suggests that either technique may be performed with similar biomechanical results at initial fixation under these loading conditions.

Function of the anterior cruciate ligament after unicompartmental knee arthroplasty: an in vitro robotic study

The objective of this study was to investigate the role of the anterior cruciate ligament (ACL) in the anterior-posterior (AP) stability of the knee after unicompartmental knee arthroplasty (UKA). AP tibial loads were applied to human cadaveric knee specimens using a robotic testing system. After UKA, the knee exhibited tibial translations similar to that of the native knee, and the forces in the ACL were also similar to those seen in the native knee. The ACL-deficient knee after UKA exhibited significantly greater anterior tibial translations than the native knee and the knee after UKA with an intact ACL. These data suggest that medial UKA does not alter the anterior stability of the knee, but a functional ACL is necessary to ensure normal stability after UKA.

The effect of posterior cruciate ligament reconstruction on patellofemoral contact pressures in the knee joint under simulated muscle loads

BACKGROUND

The mechanism of cartilage degeneration in the patellofemoral joint (PFJ) and medial compartment of the knee following posterior cruciate ligament (PCL) injury remains unclear. PCL reconstruction has been recommended to restore kinematics and prevent long-term degeneration. The effect of current reconstruction techniques on PFJ contact pressures is unknown.

PURPOSE

To measure PFJ contact pressures after PCL deficiency and reconstruction.

METHOD

Eight cadaveric knees were tested with the PCL intact, deficient, and reconstructed. Contact pressures were measured at 30 degrees, 60 degrees, 90 degrees, and 120 degrees of flexion under simulated muscle loads. Knee kinematics were measured by a robotic testing system, and the PFJ contact pressures were measured using a thin film transducer. A single bundle achilles tendon allograft was used in the reconstruction.

RESULTS

PCL deficiency significantly increased the peak contact pressures measured in the PFJ relative to the intact knee under both an isolated quadriceps load of 400 N and a combined quadriceps/hamstrings load of 400 N/200 N. Reconstruction did not significantly reduce the increased contact pressures observed in the PCL-deficient knee.

CONCLUSION

The elevated contact pressures observed in the PCL-deficient knee and reconstructed knee might contribute to the long-term degeneration observed in both the non-operatively treated and PCL-reconstructed knees.

Surgical treatment of posterior cruciate ligament and posterolateral corner injuries. An anatomical, biomechanical and clinical review

The posterior cruciate ligament has become an increasingly popular subject of orthopaedic research and debate. While biomechanical studies have shown its role as major stabilizer of the knee, clinical studies have shown its increasing incidence. Furthermore, injuries to posterolateral structures are frequently encountered and failure to recognize and treat this associated injury may lead to stretching or failure of the cruciate reconstruction. Surgical reconstruction of isolated/combined injuries is now more effective than before and different technical options are now available for the surgeon, even if much work remains ahead of us as we try to understand how to successfully treat these complex knee injuries.

Measurement of posterior tibial translation in the posterior cruciate ligament-reconstructed knee: significance of the shift in the reference position

BACKGROUND

The measurement of anterior or posterior tibial translation depends on the existence of a repeatable and accurate reference position of the knee from which the corresponding translation is measured.

HYPOTHESIS

Clinical measurements of posterior tibial translation alone do not accurately reflect the laxity of posterior cruciate ligament-reconstructed knees.

STUDY DESIGN

Controlled laboratory study.

METHODS

Ten human cadaveric knees were tested by using a robotic/universal force-moment sensor testing system. The reference positions and the resulting kinematics in response to a 134-N anterior-posterior tibial load were determined for the intact and reconstructed knees. Posterior cruciate ligament reconstruction was performed with the graft tensioned and fixed at two different positions: 1) 90 degrees of knee flexion with a 134-N anterior tibial load and 2) full extension with no load.

RESULTS

Posterior cruciate ligament reconstruction with graft fixation at full extension with no load resulted in anterior shift of the reference position by 1.5 to 3.2 mm. The reconstruction resulted in an overconstrained knee with significantly decreased total anterior-posterior translation of 2.6 to 3.2 mm. However, the posterior tibial translation measured was not significantly different from that of the intact knee. Posterior cruciate ligament reconstruction with graft fixation performed at 90 degrees of flexion with a 134-N anterior tibial load resulted in kinematics similar to those of the intact knee.

CONCLUSION

Posterior tibial translations that are measured clinically can be misleading because the reference position of the knee can be shifted significantly after posterior cruciate ligament reconstruction.

CLINICAL RELEVANCE

The measurement of total anterior-posterior translation may be a more accurate way to assess kinematics of the reconstructed knee.

On the coupling between anterior and posterior cruciate ligaments, and knee joint response under anterior femoral drawer in flexion: a finite element study

OBJECTIVE

To investigate the extent of coupling between the anterior and posterior cruciate ligaments as well as the role of the posterior cruciate ligament in the knee joint response under anterior femoral force at different flexion angles.

DESIGN

A developed finite element model of the tibiofemoral joint is used to perform non-linear elastostatic analyses.

BACKGROUND

The structural properties of the posterior cruciate ligament subsequent to an injury (either left untreated or replaced by a graft) would likely change, an event that alters the function of not only the ligament itself but also the other intact cruciate ligament and the entire joint.

METHODS

The model consists of two bony structures and their articular cartilage layers, menisci and four principal ligaments. Under 100 N anterior femoral load at different flexion angles from 0 degrees to 90 degrees, kinematics, forces in ligaments and contact forces in the fully unconstrained joint were computed in intact cases and following alterations in joint ligaments.

RESULTS

Collateral ligaments were the primary structures to resist the force at full extension under 100 N anterior femoral load with a moderate contribution from the posterior cruciate ligament. With joint flexion up to 90 degrees, however, force in the posterior cruciate ligament substantially increased whereas that in collateral ligaments diminished.

CONCLUSIONS

A remarkable coupling was found between the posterior cruciate ligament and the anterior cruciate ligament in flexion; a structural alteration in one of them significantly influenced the mechanical role of both ligaments and not just the one affected. A tauter or stiffer ligament increased the force in both ligaments while an excessive laxity or rupture in one diminished forces in both.

RELEVANCE

Alterations in ligament stiffness or initial tautness during reconstruction surgery or following injuries markedly influence the normal role of both cruciate ligaments. Consideration of cruciate ligaments coupled together rather than in isolation should be the rule in the management of ligament injuries towards a successful long-term outcome.

The biomechanical effect of posterior cruciate ligament reconstruction on knee joint function. Kinematic response to simulated muscle loads

BACKGROUND

The effectiveness of posterior cruciate ligament reconstruction in restoring normal kinematics under physiologic loading is unknown.

HYPOTHESIS

Posterior cruciate ligament reconstruction does not restore normal knee kinematics under muscle loading.

STUDY DESIGN

In vitro biomechanical study.

METHODS

Kinematics of knees with an intact, resected, and reconstructed posterior cruciate ligament were measured by a robotic testing system under simulated muscle loads. Anteroposterior tibial translation and internal-external tibial rotation were measured at 0 degrees, 30 degrees, 60 degrees, 90 degrees, and 120 degrees of flexion under posterior drawer loading, quadriceps muscle loading, and combined quadriceps and hamstring muscle loading.

RESULTS

Reconstruction reduced the additional posterior tibial translation caused by ligament deficiency at all flexion angles tested under posterior drawer loading. Ligament deficiency increased external rotation and posterior translation at angles higher than 60 degrees of flexion when simulated muscle loading was applied. Posterior cruciate ligament reconstruction reduced the posterior translation and external rotation observed in posterior cruciate ligament-deficient knees at higher flexion angles, but differences were not significant.

CONCLUSION

Under physiologic loading conditions, posterior cruciate ligament reconstruction does not restore six degree of freedom knee kinematics.

CLINICAL RELEVANCE

Abnormal knee kinematics may lead to development of long-term knee arthrosis.

Determination of optimal graft lengths for posterior cruciate ligament reconstruction--a theoretical analysis

Various graft materials have been used in posterior cruciate ligament (PCL) reconstruction. However, it is unclear if these grafts can reproduce the structural behavior of the PCL. This paper analyzed the effect of graft length on the structural behavior of the graft using a minimal deformation energy method. An analytical solution was obtained to determine the optimal effective graft length that can best reproduce the structural behavior of the PCL. This optimal graft length was determined as a function of the axial rigidity of the graft. Two typical grafts, bone-patella tendon-bone (BPTB) and Achilles tendon, were analyzed. The data demonstrated that in order to reproduce the PCL behavior, the effective length of a BPTB graft (10 mm width) should be 34 mm, while the Achilles tendon graft (with a cross sectional area of 55 mn2) needs to be 48 mm in length. Longer grafts result in less resistance and shorter graft increased the graft resistance. An initial graft tension cannot help recreate the overall structural behavior of the PCL. These results suggest that graft length is an important surgical variable in PCL reconstruction. An optimal reconstruction of the PCL should reproduce the structural properties of the PCL by using a graft with an optimal length.

Posterior cruciate ligament injuries in the athlete: an anatomical, biomechanical and clinical review

Recently, the posterior cruciate ligament (PCL) has become an increasingly popular subject of orthopaedic research and debate. In the past several years, anatomic and biomechanical studies have provided invaluable information concerning the structure and function of the PCL. However, many aspects of PCL injury are still not fully understood. Diagnosis of the injury is often missed because of subtlety of symptoms and clinical findings, and current management strategies of PCL injury have experienced relatively poor clinical outcomes. Controversy exists concerning the most appropriate treatment, especially in cases of isolated PCL injury. The purpose of this review is to present a complete overview of the current knowledge regarding the basic science and clinical aspects of PCL injuries, with a specific focus on the athletic population.

Biology and biomechanics

Increased participation by the general population in athletic activities leads to increased trauma to bones, joint surfaces, and soft tissues. Management and treatment of these injuries has significantly improved over the past few decades. The application of knowledge gained from basic science research in biology and biomechanics has continuously contributed to that. Biological advances have been made in the field of gene therapy, cell therapy, and tissue engineering. Certainly, the greatest focus is bone and cartilage research that will lead to improved fracture repair in the traumatic injured population, as well as prevention of early osteoarthritic changes in the injured athletic population. In biomechanical research, contributions have been made to further understand kinematic behavior of joints that will lead to improved ligament reconstruction techniques and rehabilitation regimens. Various fixation techniques and several different ligament reconstruction techniques have been studied and validated. In the future, improved understanding of ligament healing, graft incorporation, and revascularization will lead to improved outcome of surgical reconstruction techniques in orthopaedic sports medicine. Exciting research has been performed over the past years and will be reviewed in this article.