Lateral soft-tissue structures contribute to cruciate-retaining total knee arthroplasty stability

Evaluation of a novel robotic testing method for stability and kinematics of total knee arthroplasty

PURPOSE

This work developed a novel preclinical test of total knee replacements (TKRs) in order to explain TKR instability linked to patient dissatisfaction. It was hypothesized that stability tests on the isolated moving prostheses would provide novel comparative data on the stability and kinematics among TKR designs.

METHODS

Three TKR designs, DePuy Synthes Attune MS, Stryker Triathlon and Zimmer Biomet Persona MC, were assessed using a robotic arm while flexing-extending 0-140°. Tests imposed 710 N body weight combined with three tibial loads: no anterior-posterior (AP) force, 90 N anterior or 90 N posterior force. Other load effects were minimized and the kinematics was recorded. Each implant was tested six times to investigate the repeatability of the method. Data were analysed using statistical parametric mapping with one-way analysis of variance (ANOVA). If significance was found (p < 0.05), post hoc t tests with Bonferroni correction were used to contrast groups.

RESULTS

Significant differences were found throughout flexion-extension. Femoral rollback, AP stability, coupled internal-external rotation and AP position (roll-back) were all influenced by implant design. AP stability of the TKRs reduced with flexion reaching Attune 15 mm, Persona 13 mm and Triathlon 21 mm at 140° flexion. Tractive rolling significantly affected kinematics in the less congruent Triathlon design, with 6 mm different paths between flexion and extension motion (p < 0.05 across 5-100°). Paradoxical anterior femoral sliding in early flexion (0-40°) occurred in Persona and Triathlon designs.

CONCLUSIONS

The novel testing technique provides, for the first time, comparative data on the inherent stability and kinematics of the TKR implants themselves across the arc of flexion-extension, independent of variables including soft tissue behaviour and surgical technique. The data show how much each prosthesis can contribute to the stability and motion of the implanted knee. Similar data from a wider range of designs will enable more informed decisions regarding implant design choice, aiming to reduce the prevalence of TKR instability in patients.

LEVEL OF EVIDENCE

Controlled laboratory study.

Is Popliteus Tendon a Redundant Structure in Total Knee Arthroplasty?

Background

Many studies have shown that injury to the popliteus tendon has little consequence for the static stability of the knee following total knee arthroplasty (TKA). However, very few studies have evaluated the effect of intraoperative iatrogenic popliteus tendon injury on the patient-reported outcome measures (PROMs) following TKA. This study aimed to determine the incidence of iatrogenic popliteus tendon injury in our subset of the population and to find out its effect on PROMs.

Methods

100 consecutive osteoarthritic varus knees with flexion deformities less than 20° were operated upon by a single senior experienced arthroplasty surgeon. Patients were assessed intraoperatively for any iatrogenic popliteus tendon injury, the injury site, and the amount of injury which was quantified and graded. PROMs applied for assessment at 1-year follow-up were Knee Society Score (KSS 1), Knee Function Score (KSS 2), and Western Ontario and McMaster University Osteoarthritis Index (WOMAC).

Results

17% of cases had an iatrogenic popliteus tendon injury. Thirteen had grade II injuries, whereas four had grade III injuries. There was no statistical significance in post-operative knee mobility and PROMs among those with popliteus tendon injury versus non-injured patients.

Conclusion

The incidence of iatrogenic popliteus tendon injury is higher than what we expected. The tendon injury remains a risk, but it is unclear how the popliteus tendon injury will affect patients after the TKA. In our series, such an injury during knee replacement does not affect the functioning of the knee in the short term; however, a long-term follow-up is warranted.

Medial-pivot total knee arthroplasty enhances tibiofemoral axial rotation stability in weight-bearing mid-range flexion compared to posterior-stabilised system

PURPOSE

Total knee arthroplasty (TKA) stands as a primary intervention for severe knee ailments, yet concerns remain regarding postoperative patient satisfaction and flexion instability. This study aims to evaluate the in-vivo kinematics of medial-pivot (MP) and posterior-stabilised (PS) designs during step-up activity, in comparison to the kinematics of the nonoperated contralateral knee.

METHODS

Sixteen patients with PS-TKA and 14 with MP-TKA were retrospectively examined. Clinical outcomes were assessed using patient-completed questionnaires. Motion during step-up was captured using a dual fluoroscopic system. Statistical analysis was applied to evaluate the in-vivo tibiofemoral six-degree-of-freedom kinematics and articular contact positions between the two groups.

RESULTS

Despite being older, patients in the MP group reported higher postoperative subjective scores for weight-bearing functional activities. The axial rotation centres of MP-TKA located on the medial tibial plateau exhibited less variance compared to PS-TKA and contralateral knees. Compared to the contralateral knee (contralateral to medial-pivot [C-MP] or contralateral to posterior-stabilised [C-PS]), the MP group exhibited limited range of motion in terms of anteroposterior translation (MP: 3.6 ± 1.3 mm vs. C-MP: 7.4 ± 2.5 mm, p < 0.01) and axial rotation (MP: 6.6 ± 1.9° vs. C-MP: 10.3 ± 4.9°, p = 0.02), as well as in the PS group for anteroposterior translation (PS: 3.9 ± 1.7 mm vs. C-PS: 7.2 ± 3.7 mm, p < 0.01).

CONCLUSION

The MP group with better postoperative ratings demonstrated a more stable MP axial rotation pattern during step-up activity compared to the PS group, underscoring the pivotal role of prosthetic design in optimising postoperative rehabilitation and functional recovery.

LEVEL OF EVIDENCE

Level III.

Anterolateral knee complex considerations in contemporary anterior cruciate ligament reconstruction and total knee arthroplasty: a systematic review

The anterolateral ligament (ALL) was first described in 1879 in the context of Segond fractures, which correlate with a 75-100% chance of an anterior cruciate ligament (ACL) tear or a 66-75% chance of a meniscal tear. The purpose of this paper is to provide an updated comprehensive review on the anterolateral ligament complex of the knee focusing on the: (1) anatomy of the ALL/ALC; (2) associated biomechanics/function; and (3) important surgical considerations in contemporary anterior cruciate ligament (ACL) reconstruction and total knee arthroplasty (TKA). A systematic review of studies on ALL was conducted on Pubmed/MEDLINE and Cochrane databases (May 7th, 2020 to February 1st, 2022), with 20 studies meeting inclusion/exclusion criteria. Studies meeting inclusion criteria were anatomical/biomechanical studies assessing ALL function, cadaveric and computer simulations, and comparative studies on surgical outcomes of ALLR (concomitant with ACL reconstruction). Eight studies were included and graded by MINOR and Newcastle-Ottawa scale to identify potential biases. The anatomy of the ALL is part of the anterolateral ligament complex (ALC), which includes the superficial/deep iliotibial band (including the Kaplan fiber system), iliopatellar band, ALL, and anterolateral capsule. Multiple biomechanical studies have characterized the ALC as a secondary passive stabilizer in resisting tibial internal rotation. Given the role of the ALC in resisting internal tibial rotation, lateral extra-articular procedures including ALL augmentation may be considered for chronic ACL tears, ACL revisions, and a high-grade pivot shift test. In the context of TKA, in the event of injury to the ALC, a more constrained implant or soft-tissue reconstruction may be necessary to restore appropriate knee stability.

Radiographic Findings in Flexion Instability after Total Knee Arthroplasty

Flexion instability (FI) is one of the leading causes of knee pain and revision surgery. Generally, the biomechanical etiology is considered to be a larger flexion than extension gap. This may be due to mismatch of components sizes to the bone or malalignment. Other factors such as muscle weakness may also play a role, and the diagnosis of FI after total knee arthroplasty (TKA) relies on a combination of patient's complaints during stair descent or walking and physical examination findings. Our study examines the role of implant positioning and sizes in the diagnosis of FI. A retrospective review of 20 subjects without perceived FI and 13 patients diagnosed with FI after TKA was conducted. Knee injury and osteoarthritis outcome scores (KOOS) were documented, and postoperative radiographs were examined. Measurements including included tibial slope, condylar offset, femoral joint line elevation along with surrogate soft-tissue measures for girth and were compared between groups. The FI group was found to have a significantly lower KOOS score compared with the non-FI group (55.6 vs. 73.5; p = 0.009) as well as smaller soft-tissue measurements over the pretubercle region (6.0 mm vs. 10.6 mm; p = 0.007). Tibial slope, condylar offset ratios, and femoral joint line elevation were not significantly different between the FI and non-FI groups. We noted a significant difference in tibial slope in posterior-stabilized implants in subjects with and without FI (6.4° vs. 1.5°; p = 0.003). Radiographic measurements consistent with malalignment were not indicative of FI. X-ray measurements alone are not sufficient to conclude FI as patient symptoms, and clinical examinations remain the key indicators for diagnosis. Radiographic findings may aid in surgeon determination of an underlying cause for an already identified FI situation and help in planning revision surgery.

Coronal Laxity at Flexion is Larger After Posterior-Stabilized Total Knee Arthroplasty Than With Cruciate-Retaining Procedures

BACKGROUND

It is unclear whether coronal stability differs between cruciate-retaining (CR) and posterior-stabilized (PS) total knee arthroplasty (TKA). The purpose of this study was to compare coronal laxity, radiological, and clinical outcomes between CR-TKA and PS-TKA.

METHODS

Seventy five CR-TKAs and 72 PS-TKAs with a minimum 2-year follow-up were retrospectively evaluated. Coronal laxity was assessed at knee extension and 80° of flexion on varus and valgus stress radiographs. Radiological evaluation included femoral-tibial angle, hip-knee-ankle angle, and positions of femoral and tibial components. Clinical evaluation included the modified Hospital for Special Surgery score, the Western Ontario and McMaster Universities Osteoarthritis index, and range of motion.

RESULTS

PS-TKA resulted in significantly larger varus, valgus, and total laxities at 80° flexion (P = .034, .031, and 0.001, respectively) compared with CR-TKA, while no significant difference was found at extension (P = .513, .964, and .658, respectively). No statistical difference was found in radiological and clinical outcomes between CR-TKA and PS-TKA, but the functional scores were slightly better in CR-TKA. There were adverse correlations between varus laxity at flexion and the Western Ontario and McMaster Universities Osteoarthritis index, the modified Hospital for Special Surgery score, and range of motion (r = 0.933, -0.229, -0.472, respectively).

CONCLUSION

Coronal laxity at 80° of flexion was larger after PS-TKA than CR-TKA. In addition, clinical outcomes were adversely affected by the larger varus laxity at flexion. Care should be taken to maintain the coronal stability, especially at flexion, during surgery to obtain better patient-reported outcomes.

LEVEL OF EVIDENCE

Level III.

Modelling osteoarthritis in mice via surgical destabilization of the medial meniscus with or without a stereomicroscope

Aims

To evaluate inducing osteoarthritis (OA) by surgical destabilization of the medial meniscus (DMM) in mice with and without a stereomicroscope.

Methods

Based on sample size calculation, 70 male C57BL/6 mice were randomly assigned to three surgery groups: DMM aided by a stereomicroscope; DMM by naked eye; or sham surgery. The group information was blinded to researchers. Mice underwent static weightbearing, von Frey test, and gait analysis at two-week intervals from eight to 16 weeks after surgery. Histological grade of OA was determined with the Osteoarthritis Research Society International (OARSI) scoring system.

Results

Surgical DMM with or without stereomicroscope led to decrease in the mean of weightbearing percentages (-20.64% vs -21.44%, p = 0.792) and paw withdrawal response thresholds (-21.35% vs -24.65%, p = 0.327) of the hind limbs. However, the coefficient of variation (CV) of weight-bearing percentages and paw withdrawal response thresholds in naked-eye group were significantly greater than that in the microscope group (19.82% vs 6.94%, p < 0.001; 21.85% vs 9.86%, p < 0.001). The gait analysis showed a similar pattern. Cartilage degeneration was observed in both DMM-surgery groups, evidenced by increased OARSI scores (summed score: 11.23 vs 11.43, p = 0.842), but the microscope group showed less variation in OARSI score than the naked-eye group (CV: 21.03% vs 32.44%; p = 0.032).

Conclusion

Although surgical DMM aided by stereomicroscope is technically difficult, it produces a relatively more homogeneous OA model in terms of the discrete degree of pain behaviours and histopathological grading when compared with surgical DMM without stereomicroscope. Cite this article: Bone Joint Res 2022;11(8):518–527.

A constrained-condylar fixed-bearing total knee arthroplasty is stabilised by the medial soft tissues

PURPOSE

Revision constrained-condylar total knee arthroplasty (CCK-TKA) is often used to provide additional mechanical constraint after failure of a primary TKA. However, it is unknown how much this translates to a reliance on soft-tissue support. The aim of this study was therefore to compare the laxity of a native knee to the CCK-TKA implanted state and quantify how medial soft-tissues stabilise the knee following CCK-TKA.

METHODS

Ten intact cadaveric knees were tested in a robotic system at 0°, 30°, 60° and 90° flexion with ± 90  N anterior-posterior force, ± 8 Nm varus-valgus and ± 5 Nm internal-external torques. A fixed-bearing CCK-TKA was implanted and the laxity tests were repeated with the soft tissues intact and after sequential cutting. The deep and superficial medial collateral ligaments (dMCL, sMCL) and posteromedial capsule (PMC) were sequentially transected and the percentage contributions of each structure to restraining the applied loads were calculated.

RESULTS

Implanting a CCK-TKA did not alter anterior-posterior laxity from that of the original native knee, but it significantly decreased internal-external and varus-valgus rotational laxity (p < 0.05). Post CCK-TKA, the sMCL restrained 34% of the tibial displacing load in anterior drawer, 16% in internal rotation, 17% in external rotation and 53% in valgus, across the flexion angles tested. The dMCL restrained 11% of the valgus rotation moment.

CONCLUSIONS

With a fully-competent sMCL in-vitro, a fixed-bearing CCK-TKA knee provided more rotational constraint than the native knee. The robotic test data showed that both the soft-tissues and the semi-constrained implant restrained rotational knee laxity. Therefore, in clinical practice, a fixed-bearing CCK-TKA knee could be indicated for use in a knee with lax, less-competent medial soft tissues.

LEVEL OF EVIDENCE

Controlled laboratory study.

Posterior capsular release is a biomechanically safe procedure to perform in total knee arthroplasty

PURPOSE

Surgeons may attempt to strip the posterior capsule from its femoral attachment to overcome flexion contracture in total knee arthroplasty (TKA); however, it is unclear if this impacts anterior-posterior (AP) laxity of the implanted knee. The aim of the study was to investigate the effect of posterior capsular release on AP laxity in TKA, and compare this to the restraint from the posterior cruciate ligament (PCL).

METHODS

Eight cadaveric knees were mounted in a six degree of freedom testing rig and tested at 0°, 30°, 60° and 90° flexion with ± 150 N AP force, with and without a 710 N axial compressive load. After the native knee was tested, a deep dished cruciate-retaining TKA was implanted and the tests were repeated. The PCL was then cut, followed by releasing the posterior capsule using a curved osteotome.

RESULTS

With 0 N axial load applied, cutting the PCL as well as releasing the posterior capsule significantly increased posterior laxity compared to the native knee at all flexion angles, and CR TKA states at 30°, 60° and 90° (p < 0.05). However, no significant increase in laxity was found between cutting the PCL and subsequent PostCap release (n.s.). In anterior drawer, there was a significant increase of 1.4 mm between cutting the PCL and PostCap release at 0°, but not at any other flexion angles (p = 0.021). When a 710 N axial load was applied, there was no significant difference in anterior or posterior translation across the different knee states (n.s.).

CONCLUSIONS

Posterior capsular release only caused a small change in AP laxity compared to cutting the PCL and, therefore, may not be considered detrimental to overall AP stability if performed during TKA surgery.

LEVEL OF EVIDENCE

Controlled laboratory study.