Quantitative measurement of patellofemoral joint stability: force-displacement behavior of the human patella in vitro

Inferior patellar mobility before and after knee arthroplasty: A comparison with healthy knees

PURPOSE

The aim of this study was to evaluate patellar mobility in patients before and after knee arthroplasty (KA) and compare it with that of healthy subjects. It was hypothesised that patellar mobility is diminished in patients with osteoarthritis (OA) and remains unchanged after KA.

METHODS

A total of 101 patients (59 females and 42 males) with a mean age of 70.9 ± 9.9 years underwent KA and were compared with 25 healthy individuals (seven females and 18 males) with a mean age of 32.3 ± 9.3 years. Mediolateral patellar displacement was measured by applying a force of 10 N, and the medial and lateral patellar shifts were recorded separately using a validated novel patellostabilometer. Patients were examined preoperatively and at 3 months postoperatively, assessing the range of knee motion and the clinical and functional status based on the Oxford Knee Score (OKS), Kujala Score, subjective Knee Society Score (sKSS), Forgotten Joint Score (FJS) and Western Ontario and McMaster Universities Arthritis Index (WOMAC).

RESULTS

Total patellar displacement was 42.1 ± 6 mm for healthy subjects, 31 ± 6 mm before surgery and 32.8 ± 7.8 mm after surgery in osteoarthritic patients (p < 0.01). The mean lateral patellar shift differed significantly between healthy individuals (17.9 ± 4 mm) and osteoarthritic patients (15.1 ± 6 mm) (p < 0.01). The mean medial patellar mobility of healthy individuals (24.2 ± 7 mm) was significantly greater than that of osteoarthritic patients (15.8 ± 4.8 mm) (p < 0.01). All scores improved significantly postoperatively. No correlation was found between patellar mobility and OKS, Kujala Score, sKSS, FJS and WOMAC (r = -0.11). Improvement in patellar mobility also showed no correlation with clinical outcomes according to OKS, Kujala Score, sKSS, FJS and WOMAC (r = 0.08).

CONCLUSION

This study has demonstrated reduced patellar mobility in patients with OA. While patellar mobility significantly improved after KA, it may not hold clinical significance (p = 0.04). No impact on clinical outcome can be expected when the presurgical patella mobility is preserved in KA.

LEVEL OF EVIDENCE

Level IV.

The Adductor Sling Technique for Pediatric Medial Patellofemoral Ligament Reconstruction Better Resists Dislocation Loads When Compared With Adductor Transfer at Time Zero in a Cadaveric Model

Purpose

To characterize the ability of the intact medial patellofemoral ligament (MPFL) and the adductor transfer and adductor sling MPFL reconstruction techniques to resist subluxation and dislocation in a cadaveric model.

Methods

Nine fresh-frozen cadaveric knees were placed on a custom testing fixture with the femur fixed parallel to the floor, the tibia placed in 20° of flexion, and the patella attached to a load cell. The patella was displaced laterally, and subluxation load (in newtons), dislocation load (in newtons), maximum failure load (in newtons), patellar displacement at failure, and mode of failure were recorded. Testing was conducted with the MPFL intact and after the adductor sling and adductor transfer reconstruction techniques. Statistical analysis was completed using 1-way repeated-measures analysis of variance with the Holm-Šidák post hoc test.

Results

The subluxation load was not significantly different between groups. The native MPFL dislocation load was significantly higher than the dislocation loads of both reconstruction techniques, but no significant difference between the dislocation loads of the 2 reconstruction techniques occurred. The native MPFL failure load was significantly higher than the failure loads of both reconstruction techniques. The adductor sling failure load was significantly higher than the adductor transfer failure load. The mode of failure varied across groups. The native MPFL failed by femoral avulsion, patellar avulsion, and midsubstance tear. The main mode of failure for adductor transfer was pullout, whereas failure for the adductor sling technique most often occurred at the sutures. Most of the native MPFLs and all adductor sling reconstructions failed after dislocation. The adductor transfer reconstructions were much more variable, with failures spanning from before subluxation through dislocation.

Conclusions

Our cadaveric model showed that neither the adductor transfer technique nor the adductor sling technique restored failure load to that of the native condition. There was no significant difference in the subluxation or dislocation loads between the 2 MPFL reconstructions, but the adductor sling technique resulted in a higher load to failure. The adductor transfer technique frequently failed before subluxation or dislocation when compared with the adductor sling technique and the native MPFL.

Clinical Relevance

The best technique for MPFL reconstruction in patients with open physes is a topic of debate. Given the long-term consequences of MPFL injury and potential for growth plate disturbance, it is important to study MPFL reconstruction techniques thoroughly, including in the laboratory setting.

Reconstruction of medial patellofemoral ligament with adductor magnus tendon for recurrent patellar dislocation in children: a retrospective comparative cohort study

BACKGROUND

The purpose of current retrospective study was to explore the outcomes of using the adductor magnus tendon to reconstruct the medial patellofemoral ligament in the treatment of recurrent patellar dislocation in children.

METHOD

Thirty-two children with recurrent patellar dislocation were selected. Sixteen cases in the conservative group, seven males and nine females, with an average age of 11.81 ± 1.28 years; sixteen cases in the surgical group, eight males and eight females, with an average age of 11.56 ± 1.15 years. All patients had no surgery history. The IS index (> 1.2), Q angle (> 20°) and tibial tubercle-femoral trochlear groove (TT-TG) distance (> 20 mm) were measured by X-ray and MRI. The conservative group was treated with closed reduction and a brace, and the surgical group received surgical treatment. Two years after surgery, congruence angle (CA) (- 6° to 6°) and lateral patellofemoral angle (LPFA) (7.7°-18.7°) were measured by X-ray image and all children were evaluated based on Kujala and Lysholm scores. The re-dislocation rate was recorded. Analysis was performed by t test and chi-square with the statistical SPSS software. P < 0.05 was considered a statistically significant difference. Furthermore, we measured the length (mm) of the adductor tendon and MPFL in three knee cadaveric specimens, and also observed the positional relationship between the two structures.

RESULT

There were no significant differences in sex, age, injury site between groups (P > 0.05). Patients in the two groups were followed up for 2 years in average. Among the 16 cases in the conservative group, 7 cases (43.75%) had recurrence of patellar dislocation, while none of recurrence in the surgical group (P < 0.05). The Lysholm score of the surgical group (94.63 ± 8.99) was significantly better than that of the conservative group (79.31 ± 18.90), and the Kujala score of the surgery group (95.25 ± 10.32) was also significantly better than that of the conservative group (77.06° ± 14.34°) (P < 0.05). The CA and LPFA of the two groups of patients after treatment were significantly recovered. The CA (- 5.81° ± 7.90°) in the surgical group was significantly better than that in the conservative group (20.94° ± 8.21°), and the LPFA (6.44° ± 3.22°) was also significantly better than that in the conservative group (- 9.18 ± 11.08), and the difference is statistically significant (P < 0.05). We found it through autopsy that adductor magnus tendon was 124.33 ± 1.53 mm long, MPFL was 48.67 ± 2.08 mm, and the femoral insertion of the adductor magnus tendon was adjacent to the MPFL femoral insertion.

CONCLUSION

Reconstruction of Medial patellofemoral ligament with the adductor magnus tendon, fixing with PEEK suture anchors on the patellar side, can achieve satisfactory results in the treatment of children with recurrent patellar dislocation. Compared with conservative treatment, the rate of recurrence is lower and the stability of the patella is better.

Mid-term study on the effects of arthroscopic discoid lateral meniscus plasty on patellofemoral joint: An observational study

In the present study, we aimed to investigate the clinical outcomes of arthroscopic discoid lateral meniscus (DLM) plasty and the adaptive changes in the patellofemoral joint after surgery. From September 2010 to March 2012, 25 patients with DLM injuries who underwent arthroscopic meniscus plasty were enrolled in the prospective study. All patients underwent clinical evaluation before the operation and at the last follow-up, and imaging evaluation was performed by upright magnetic resonance imaging before and 1 month after the operation as well as at the last follow-up. Clinical evaluation included Lysholm score, Kujala score, McMurray's sign, patellar mobility, patella grind test, and quadriceps atrophy. Imaging evaluation included bisect offset index, patella tilt angle (PTA), and cartilage damage. Lysholm score, Kujala score, McMurray's sign, and quadriceps atrophy at the last follow-up were significantly improved compared with the preoperative levels (P < .05). At the last follow-up, there were no statistical differences in patella mobility and patella grind test compared with the preoperative levels. In addition, bisect offset index and PTA showed a dynamic trend of rising and then falling over time (P < .05). At 1 month after the operation, bisect offset index and PTA were significantly increased compared with the preoperative levels or the values at the last follow-up (P < .05), while there were no differences between the preoperation and the last follow-up. Cartilage damage became worse with time (P < 0.05), and the 2 were positively correlated (Spearman = 0.368). At the last follow-up, the degree of cartilage damage was significantly increased compared with the preoperative level (P < .017), while there was no significant difference between the 1-month postoperative grade and the preoperational grade or the last follow-up grade. The effect of arthroscopic DLM plasty on the patellofemoral joint was dynamic, with the position of the patella deviating in the early stages and recovering in the mid-term, especially when the knee was in the biomechanical standing position. In addition, the patellofemoral joint cartilage might undergo accelerated degeneration after the operation, while the mid-term effect of the operation was positive, and the patellofemoral joint function was acceptable.

Computational biomechanics of human knee joint in stair ascent: Muscle-ligament-contact forces and comparison with level walking

About a third of knee joint disorders originate from the patellofemoral (PF) site that makes stair ascent a difficult activity for patients. A detailed finite element model of the knee joint is coupled to a lower extremity musculoskeletal model to simulate the stance phase of stair ascent. It is driven by the mean of measurements on the hip-knee-ankle moments-angles as well as ground reaction forces reported in healthy individuals. Predicted muscle activities compare well to the recorded electromyography data. Peak forces in quadriceps (3.87 BW, body weight, at 20% instance in our 607 N subject), medial hamstrings (0.77 BW at 20%), and gastrocnemii (1.21 BW at 80%) are estimated. Due to much greater flexion angles-moments in the first half of stance, large PF contact forces (peak of 3.1 BW at 20% stance) and stresses (peak of 4.83 MPa at 20% stance) are estimated that exceed their peaks in level walking by fourfold and twofold, respectively. Compared with level walking, ACL forces diminish in the first half of stance but substantially increase later in the second half (peak of 0.76 BW at 75% stance). Under nearly similar contact forces at 20% of stance, the contact stress on the tibiofemoral (TF) medial plateau reaches a peak (9.68 MPa) twice that on the PF joint suggesting the vulnerability of both joints. Compared with walking, stair ascent increases peak ACL force and both peak TF and PF contact stresses. Reductions in the knee flexion moment and/or angle appear as a viable strategy to mitigate internal loads and pain.

The influence of patellofemoral stabilisation surgery on joint congruity: an MRI surface mapping study

BACKGROUND

In the unstable patellofemoral joint (PFJ), the patella will articulate in an abnormal manner, producing an uneven distribution of forces. It is hypothesised that incongruency of the PFJ, even without clinical instability, may lead to degenerative changes. The aim of this study was to record the change in joint contact area of the PFJ after stabilisation surgery using an established and validated MRI mapping technique.

METHODS

A prospective MRI imaging study of patients with a history of PFJ instability was performed. The patellofemoral joints were imaged with the use of an MRI scan during active movement from 0° through to 40° of flexion. The congruency through measurement of the contact surface area was mapped in 5-mm intervals on axial slices. Post-stabilisation surgery contact area was compared to the pre-surgery contact area.

RESULTS

In all, 26 patients were studied. The cohort included 12 male and 14 female patients with a mean age of 26 (15-43). The greatest mean differences in congruency between pre- and post-stabilised PFJs were observed at 0-10 degrees of flexion (0.54 cm² versus 1.18 cm², p = 0.04) and between 11° and 20° flexion (1.80 cm² versus 3.45 cm²; p = 0.01).

CONCLUSION

PFJ stabilisation procedures increase joint congruency. If a single axial series is to be obtained on MRI scan to compare the pre- and post-surgery joint congruity, the authors recommend 11° to 20° of tibiofemoral flexion as this was shown to have the greatest difference in contact surface area between pre- and post-operative congruency.

The quantitative influence of current treatment options on patellofemoral stability in patients with trochlear dysplasia and symptomatic patellofemoral instability - a finite element simulation

BACKGROUND

Trochlear dysplasia is highly associated with patellofemoral instability. The goal of conservative and surgical treatment is to stabilize the patella while minimizing adverse effects. However, there is no literature investigating the quantitative influence of different treatment options on patellofemoral stability in knees with trochlear dysplasia. We created and exploited a range of finite element models to address this gap in knowledge.

METHODS

MRI data of 5 knees with trochlear dysplasia and symptomatic patellofemoral instability were adapted into this previously established model. Vastus medialis obliquus strengthening as well as double-bundle medial patellofemoral ligament reconstruction and the combination of medial patellofemoral ligament reconstruction and trochleoplasty were simulated. The force necessary to dislocate the patella by 10 mm and fully dislocate the patella was calculated in different flexion angles.

FINDINGS

Our model predicts a significant increase of patellofemoral stability at the investigated flexion angles (0°-45°) for a dislocation of 10 mm and a full dislocation after medial patellofemoral ligament reconstruction and the combination of medial patellofemoral ligament reconstruction and trochleoplasty compared to trochleodysplastic (P = 0.01) and healthy knees (P = 0.01-0.02). Vastus medialis obliquus strengthening has a negligible effect on patellofemoral stability.

INTERPRETATIONS

This is the first objective quantitative biomechanical evidence supporting the place of medial patellofemoral ligament reconstruction and medial patellofemoral ligament reconstruction combined with trochleoplasty in patients with symptomatic patellofemoral instability and trochlear dysplasia type B. Vastus medialis obliquus strengthening has a negligible effect on patellar stability at a low total quadriceps load of 175 N.

A patient-specific finite element analysis of the anterior cruciate ligament under different flexion angles

BACKGROUND

The main responsibility of the anterior cruciate ligament (ACL) is to restore normal knee kinematics and kinetics. Although so far different research has been carried out to measure or quantify the stresses and strains in the ACL experimentally or numerically, there is still a paucity of knowledge in this regard under different flexion angles of the tibiofemoral knee joint.

OBJECTIVE

Understanding the stresses and strains within the ACL under various loading and boundary conditions may have a key asset for the development of an optimal surgical treatment of ACL injury that can better restore normal knee function. This study aimed to calculate the stresses and strains within the ACL under different flexion angles using a patient-specific finite element (FE) model of the human tibiofemoral knee joint.

METHODS

A patient-specific FE model of the human tibiofemoral knee joint was established using computed tomography/magnetic resonance imaging data to calculate the stresses and strains in the ACL under different flexion angles of 0, 10, 20, 30, and 45∘.

RESULTS

Although the role of the flexion angle in the induced stresses and strains of the ACL was insignificant, the highest stress and strain were observed at the flexion angle of 0∘. The concentration of the stresses and strains regardless of the flexion angles were also located at the proximal end of the ACL, where the clinical reports indicated that most ACL tearing occurs there at the femoral insertion site.

CONCLUSIONS

The results have implications not only for understanding the stresses and strains within the ACL under different flexion angles, but also for providing preliminary data for the biomechanical and medical experts in regard of the injuries which may occur to the ACL at relatively higher flexion angles.

Patellofemoral instability in trochleodysplastic knee joints and the quantitative influence of simulated trochleoplasty - A finite element simulation

BACKGROUND

Patellofemoral instability is a debilitating condition mainly affecting young patients and has been correlated with trochlear dysplasia. It can occur when the patella is insufficiently guided through its range of motion. Currently, there is no literature describing patellofemoral stability in trochleodysplastic knees and the effect of isolated trochleoplasty on patellofemoral stability.

METHODS

The effect of isolated trochleoplasty in trochleodysplastic knees of patients with symptomatic patellofemoral instability was investigated using a quasi-static finite element model. MRI data of five healthy knees were segmented, meshed and a finite element analysis was performed in order to validate the model. A second validation was performed by comparing simulated patellofemoral kinematics to in-vivo values obtained from upright- weight bearing CT scans. Subsequently, five trochleodysplastic knees were modelled before and after simulated trochleoplasty. The force necessary to dislocate the patella by 10 mm and to fully dislocate the patella was calculated in various knee flexion angles between 0 and 45°.

FINDINGS

The developed models successfully predicted outcome values within the range of reference values from literature. Lateral stability was significantly lower in trochleodysplastic knees compared to healthy knees. Trochleoplasty was determined to significantly increase the force necessary to dislocate the patella in trochleodysplastic knees to comparable values as in healthy knees.

INTERPRETATION

This is the first study to investigate lateral patellofemoral stability in patients with symptomatic patellofemoral instability and dysplasia of the trochlear groove. We confirm that patellofemoral stability is significantly lower in trochleodysplastic knees than in healthy knees. Trochleoplasty increases patellofemoral stability to levels similar to healthy.

Combined medial patellofemoral and patellotibial reconstruction with soft tissue fixation in recurrent patellar dislocation

INTRODUCTION

The medial patellofemoral and patellotibial ligaments (MPFL and MPTL) are the main passive restraints to lateral patellar translation. When nonoperative management of patellofemoral dislocations fails, surgical options can be considered to restore patellofemoral stability. Several reconstruction procedures of the MPFL with semitendinosus, gracilis, quadriceps tendon, and synthetic grafts have been described. No clear superiority of one surgical technique over another is evident.

MATERIALS AND METHODS

Patients who suffered at least two documented episodes of unilateral patellar dislocation, confirmed radiographically and at clinical examination, underwent combined MPFL and MPTL reconstruction. Patients were regularly followed-up postoperatively at 2, 4, 8, 12, and 24 weeks, and then annually for a minimum of 2.5 years. Clinical and functional evaluations were performed using the modified Cincinnati rating system and the Kujala score, while anthropometry values including thigh volume and cross-sectional area of the thigh were measured before the operation and at the latest follow-up bilaterally.

RESULTS

There were 7 males and 27 females with a mean age of 26.5 ± 10.7 years (range, 13-39 years). The mean follow-up was 3.1 years (range, 2.5-4 years). The mean modified Cincinnati score Increased from 51 ± 22 preoperatively to 90 ± 19 (P = .001). The mean Kujala scores increased from 47 ± 17 preoperatively to 82 ± 17 (P = .02), with no significant differences between patients with or without osteochondral lesions (P ≥ .05), and between male and female patients (P ≥ .08). The Insall-Salvati index was 1.1 preoperatively and remained within normal range (P = .05) at the latest follow-up.

CONCLUSION

Combined reconstruction of MPFL and MPTL using an ipsilateral autologous gracilis tendon is satisfactory and effective and can be considered as suitable management option to treat recurrent dislocation of the patella. However, randomized studies are needed to compare different techniques.

STUDY DESIGN

Case series.

Recurrent patellar dislocations in adolescents result in decreased knee flexion during the entire gait cycle

PURPOSE

To evaluate the kinematics/kinetics of the ankle, knee, hip in the sagittal plane in adolescents with recurrent patellar dislocation in comparison to a healthy control.

METHODS

Case-control study. Eighty-eight knees (67 patients) with recurrent patellar dislocation (mean age 14.8 years ± 2.8 SD) were compared to 54 healthy knees (27 individuals, 14.9 years  ± 2.4 SD). Kinematics/kinetics of ankle, knee, hip, and pelvis were captured using 3D-gait analysis (VICON, 12 cameras, 200 Hz, Plug-in-Gait, two force plates). One cycle (100%) consisted of 51 data-points. The mean of six trials was computed.

RESULTS

The loading-response increased by 0.02 s ± 0.01SE (10.8%) with dislocations (0.98% of total gait, P < 0.01). The mid-stance-phase decreased equally (P < 0.01). Dislocation decreased knee flexion during the entire gait cycle (P < 0.01), with the largest difference during mid-stance (9.0° ± 7.2 SD vs. 18.5° ± 6.7 SD). Dislocation increased plantar-flexion during loading response 4.1° ± 0.4 SE with (P < 0.01), afterward, the dorsal-extension decreased 3.2° ± 0.3 SE, (P < 0.01). Dislocation decreased hip flexion during all phases (P < 0.01). Maximal difference: 7.5° ± 0.5 SE during mid-stance. 80% of all patients developed this gait pattern. Internal moments of the ankle increased, of the knee and hip decreased during the first part of stance.

CONCLUSION

Recurrent patellar dislocation decreases knee flexion during the loading-response and mid-stance phase. A decreased hip flexion and increased plantar-flexion, while adjusting internal moments, indicate a compensation mechanism.

LEVEL OF EVIDENCE

III.

Trochleoplasty improves knee flexion angles and quadriceps function during gait only if performed bilaterally

PURPOSE

To investigate if a trochleoplasty increases knee flexion angles and extensor moments in the gait of patients with patellar instability and to compare postoperative gait to a healthy control group.

METHODS

A bilateral dislocation group (6 patients) and a unilateral dislocation group (14 patients) were treated with bilateral and unilateral trochleoplasty, respectively. Kinematics and kinetics of the lower extremity were captured using 3D-gait analysis (VICON, 12 cameras, 200 Hz, plug-in-gait, two force plates). The mean of six trials was computed. The gait cycles were compared pre to postoperatively for each group. The gait of the two groups was compared to each other and the gait of a healthy population (54 knees).

RESULTS

After trochleoplasty, the knee flexion angles and knee extensor moments only increased in the bilateral dislocation group, whereas the gait pattern of the unilateral dislocation group remained unchanged. Compared to the healthy population, the postoperative gait pattern of the bilateral dislocation group did not differ. In contrast, knee flexion angles and extensor moments of the unilateral dislocation group were still lower.

CONCLUSION

In adolescents with bilateral recurrent patellar dislocations, trochleoplasty of both knees increases knee flexion angles and knee extensor moments comparable to normal gait. Unilateral symptomatic patients undergoing a unilateral trochleoplasty did not achieve normal walking. These findings point out that patellar instability should be considered as a bilateral problem, even in patients with unilateral dislocations.

LEVEL OF EVIDENCE

III.

Patellofemoral Mechanics: a Review of Pathomechanics and Research Approaches

PURPOSE OF REVIEW

The patellofemoral joint is a complicated articulation of the patella and femur that is prone to pathologies. The purpose of this review is to report on the current methods of investigating patellofemoral mechanics, factors that affect joint function, and future directions in patellofemoral joint research with emerging technologies and techniques.

RECENT FINDINGS

While previous hypotheses have suggested that the patella is only a moment arm extender, recent literature has suggested that the patella influences the control of knee moments and forces acting on the tibia as well as contributes to various aspects of patellar function with minimal neural input. With advancements in simulating a six-degrees-of-freedom patellofemoral joint, we have gained a better understanding of patella motion and have shown that geometry and muscle activations impact patella mechanics. Research into influences on patella mechanics from other joints such as the hip and foot has become more prevalent. In this review, we report current in vivo, in vitro, and in silico approaches to studying the patellofemoral joint. Kinematic and anatomical factors that affect patellofemoral joint function such as patella alta and tilt or bone morphology and ligaments are discussed. Moving forward, we suggest that advanced in vivo dynamic imaging methods coupled to musculoskeletal simulation will provide further understanding of patellofemoral pathomechanics and allow engineers and clinicians to design interventions to mitigate or prevent patellofemoral pathologies.

Osteochondral Fracture of Posterior Aspect of Lateral Femoral Condyle After Lateral Patella Dislocation: A Case Report

CASE

A healthy 15-year-old girl presented with osteochondral fracture at the posterior aspect of the lateral femoral condyle (LFC) associated with a right patellar dislocation after a noncontact injury. The patient remained asymptomatic 18 months after the arthroscopically assisted reduction and internal fixation of the osteochondral fracture using bioabsorbable pins and was able to eventually resume her usual activities of daily living.

CONCLUSIONS

This is the first report of an osteochondral fracture at the posterior aspect of the LFC after an acute patellar dislocation, successfully treated with arthroscopically assisted reduction and internal fixation using bioabsorbable pins. This rare injury and unique mechanism of injury have been discussed.

Computational approach to correcting joint instability in patients with recurrent patellar dislocation

Patellar dislocation is a debilitating injury common in active adolescents and young adults. Conservative treatment after initial dislocation is often recommended, but almost half of these patients continue to suffer from recurrent dislocation. The objective of this study was to compare preoperative patellofemoral joint stability with stability after a series of simulated procedures, including restorative surgery to correct to pre-injury state, generic tibial tubercle osteotomy, patient-specific reconstructive surgery to correct anatomic abnormality, less invasive patient-specific surgery, and equivalent healthy controls. Three-dimensional, subject-specific finite element models of the patellofemoral joint were developed for 28 patients with recurrent patellar dislocation. A 50 N lateral load was applied to the patella to assess the lateral stability of the patellofemoral joint at 10° intervals from 0° to 40° flexion. Medial patellofemoral ligament reconstruction, along with reconstructive procedures to correct anatomic abnormality were simulated. Of all the simulations performed, the healthy equivalent control models showed the least patellar internal-external rotation, medial-lateral translation, and medial patellofemoral ligament restraining load during lateral loading tests. Isolated restorative medial patellofemoral ligament reconstruction was the surgery that resulted in the most patellar internal-external rotation, medial-lateral translation, and medial patellofemoral ligament reaction force across all flexion angles. Patient-specific reconstruction to correct anatomic abnormality was the only surgical group to have non-significantly different results compared with the healthy equivalent control group across all joint stability metrics evaluated. Statement of clinical significance: This study suggests patient-specific reconstructive surgery that corrects underlying anatomic abnormalities best reproduces the joint stability of an equivalent healthy control when compared with the pre-injury state, generic tibial tubercle osteotomy, and less invasive patient-specific surgery. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:768-776, 2020.

Referencing the trochlear groove based on three-dimensional computed tomography imaging improves the reliability of the measurement of the tibial tuberosity-trochlear groove distance in patients with higher grades of trochlea dysplasia

BACKGROUND

To determine whether 3D-CT imaging technique is valid and reproducible compared to conventional CT measurement technique (CCT) for the detection of a femoropatellar instability.

METHODS

Patients who had undergone surgery for femoropatellar instability (patellar instability group) between 2010 and 2016 (n = 37 knees of 35 patients) were retrospectively enrolled. For the matched control group, patients who had acute anterior cruciate ligament injury (<4 weeks previously; n = 30) were recruited. Preoperative CT data had been obtained in all patients. Inter-rater reliability was calculated for both measurement protocols, and inter-method reliability was calculated between the two imaging modalities. The results are reported using intraclass correlation coefficients (ICCs) and Bland-Altman 95% limits of agreement.

RESULTS

All patients in the patellar instability group had femoral trochlear dysplasia (Dejour types A: four, B: 19, C: seven, and D: six), but no dysplasia was noted in the control group. In the patellar instability group, the CCT technique showed a poor inter-rater agreement (ICC = 0.74), and the 3D-CT technique still showed excellent inter-rater agreement (ICCs = 0.91). In the sub-analysis of the patellar instability group according to the trochlear dysplasia grade, ICCs were markedly decreased with severe trochlear dysplasia when using CCT technique; however, the 3D-CT technique could provide excellent reliability even with severe trochlear dysplasia.

CONCLUSION

The 3D-CT imaging technique for the measurement of the TT-TG distance can be suggested as a better measurement technique for patellar instability patients with bone abnormality.

Changes of mediolateral soft tissue gaps in total knee arthroplasty after suturing medial extensor in navigation

PURPOSE

Aim is to investigate the changes of mediolateral soft tissue gaps in total knee arthroplasty (TKA) after suturing medial extensor.

METHODS AND MATERIALS

We compared the differences of medial and lateral gap values that were shown by the computer navigation at 0°, 45°, 90°, and 120° knee flexion during patella in situ and during patella repaired by a towel clip on two constant sites. Fifty consecutive knees (43 patients) scheduled for TKA due to varus knee osteoarthritis, from February 2017 to May 2017, were enrolled in this prospective study.

RESULTS

The medial gaps with patella repaired were significantly lower ( p < 0.05) than the medial gaps with patella in situ at 45°, 90°, and 120° knee flexion. Differences in the medial gap were largest at 90, with the difference of 0.87 mm. Twenty-four of 50 cases (48%) showed medial gap differences of 1 mm or over, and 13 of 50 cases (26%) showed medial gap differences of 2 mm or over. The variation in the medial gap at 90° following patellar repair showed significant association (correlation coefficient = 0.78, p = 0.001) with the difference between medial and lateral gaps (medial gap - lateral gap) at 90° of patella in situ. At 90° knee flexion, when the medial and lateral gap difference in patella in situ was 1 mm or less, 73.5% (25/34) of the cases showed variation in the medial gap of less than 1 mm after patellar repair.

CONCLUSION

During TKA, while measuring the medial gap with patella in situ, overestimation might occur, especially in the position of knee flexion. Thus, reevaluation using towel clips should be considered when the medial and lateral gap difference is 1 mm or larger when patella in situ during evaluation of the medial and lateral gaps at 90° knee flexion.

Mapping the contact area of the patellofemoral joint: the relationship between stability and joint congruence

AIMS

The aim of this study was to determine and compare the congruency of the articular surface contact area of the patellofemoral joint (PFJ) during both active and passive movement of the knee with the use of an MRI mapping technique in both the stable and unstable PFJ.

PATIENTS AND METHODS

A prospective case-control MRI imaging study of patients with a history of PFJ instability and a control group of volunteers without knee symptoms was performed. The PFJs were imaged with the use of an MRI scan during both passive and active movement from 0° through to 40° of flexion. The congruency through measurement of the contact surface area was mapped in 5-mm intervals on axial slices. In all, 40 patients were studied. The case group included 31 patients with symptomatic patellofemoral instability and the control group of nine asymptomatic volunteers. The ages were well matched between the case and control groups. The mean age was 25 years (16 to 42; sd 6.9) in the case group and 26 years (19 to 32; sd 5.1) in the control group. There were 19 female and 12 male patients in the case group.

RESULTS

The unstable PFJs were demonstrably less congruent than the stable PFJs throughout the range of knee movement. The greatest mean differences in congruency between unstable and stable PFJ's were observed between 11° and 20° flexion (1.73 cm² vs 4.00 cm²; p < 0.005).

CONCLUSION

The unstable PFJ is less congruent than the stable PFJ throughout the range of knee movement studied. This approach to mapping PFJ congruency produces a measurable outcome and will allow the assessment of pre- and postoperative results following surgical intervention. This may facilitate the design of new procedures for patients with PFJ instability. If a single axial series is to be obtained on MRI scan, the authors recommend 11° to 20° of tibiofemoral flexion, as this was shown to have the greatest difference in contact surface area between the case and control groups. Cite this article: Bone Joint J 2019;101-B:552-558.

Deepening trochleoplasty and medial patellofemoral ligament reconstruction normalize patellotrochlear congruence in severe trochlear dysplasia

AIMS

The aim of this study was to evaluate cartilaginous patellotrochlear congruence and patellofemoral alignment parameters after deepening trochleoplasty in severe trochlear dysplasia.

PATIENTS AND METHODS

The study group comprised 20 patients (two male, 18 female; mean age 24 years (16 to 39)) who underwent deepening trochleoplasty and medial patellofemoral ligament (MPFL) reconstruction for the treatment of recurrent lateral patellar dislocation due to severe trochlear dysplasia (Dejour type B to D). Pre- and postoperative MRI investigations of the study group were compared with MRI data of 20 age- and gender-matched control patients (two male, 18 female; mean age 27 years (18 to 44)) regarding the patellotrochlear contact ratio, patellotrochlear contact area, posterior patellar edge-trochlear groove ratio, and patellar tilt.

RESULTS

Preoperatively, all parameters in the study group indicated significant patellar malalignment, including a reduced patellotrochlear contact ratio (mean 0.38 (0.13 to 0.59) vs mean 0.67 (0.48 to 0.88); p < 0.001), reduced contact area (mean 128 mm² (87 to 190) vs mean 183 mm² (155 to 227); p < 0.001), increased patellar lateralization (mean 0.82 (0.55 to 1.0) vs mean 0.99 (0.93 to 1.1); p < 0.001) and increased patellar tilt (mean 25.8° (8.1° to 43.0°) vs mean 9.1° (0.5° to 16.8°); p < 0.001). Postoperatively, all parameters in the study group improved significantly and reached normal values compared with the control group. The patellotrochlear contact ratio increased to a mean of 0.63 (0.38 to 0.85) (p < 0.001), the contact area increased to a mean of 187 mm² (101 to 255) (p < 0.001), the posterior patellar edge-trochlear groove ratio improved to a mean of 0.96 (0.83 to 0.91) (p < 0.001), and the patellar tilt decreased to a mean of 13.9° (8.1° to 22.1°) (p < 0.001) postoperatively.

CONCLUSION

Deepening trochleoplasty and MPFL reconstruction normalized the patellotrochlear congruence and patellofemoral alignment parameters. Modifying the dysplastic trochlea involves approximating the trochlear morphology to the shape of the patella rather than inducing a patella and trochlea mismatch. Cite this article: Bone Joint J 2019;101-B:325-330.

A cadaveric model to evaluate the effect of unloading the medial quadriceps on patellar tracking and patellofemoral joint pressure and stability

BACKGROUND

Vastus Medialis Muscles (VMM) damage has been widely identified following patellar dislocation. Rehabilitation programmes have been suggested to strengthen the VMM and reduce clinical symptoms of pain and instability. This controlled laboratory study investigated the hypothesis that reduced Vastus Medialis Obliquus (VMO) and Vastus Medialis Longus (VML) muscle tension would alter patellar tracking, stability and PFJ contact pressures.

METHODS

Nine fresh-frozen dissected cadaveric knees were mounted in a rig with the quadriceps and iliotibial band loaded to 205 N. An optical tracking system measured joint kinematics and pressure sensitive film between the patella and trochlea measured PFJ contact pressures. Measurements were repeated for three conditions: 1. With all quadriceps heads and iliotibial band (ITB) loaded; 2. as 1, but with the VMO muscle unloaded and 3. as 1, but with the VMO and VML unloaded. Measurements were also repeated for the three conditions with a 10 N lateral displacement force applied to the patella.

RESULTS

Reduction of VMM tension resulted in significant increases in lateral patellar tilt (2.8°) and translation (4 mm), with elevated lateral and reduced medial joint contact pressures from 0.48 to 0.14 MPa, and reduced patellar stability (all p < 0.05).

CONCLUSIONS

These findings provide basic scientific rationale to support the role of quadriceps strengthening to resist patellar lateral maltracking and rebalance the articular contact pressure away from the lateral facet in patients with normal patellofemoral joint anatomy.

Rehabilitation After Medial Patellofemoral Ligament Reconstruction

Patellar instability resulting from subluxation or dislocation is a painful and commonly recurring condition. Retinacular restraints control patellar tracking, limiting the movement of the patella in the trochlear groove. The medial patellofemoral ligament (MPFL) is considered the main soft tissue stabilizer against lateral displacement. Few studies of patellar instability discuss rehabilitation after MPFL reconstruction. In this review, we discuss the phases of rehabilitation after MPFL reconstruction, typical interventions by rehabilitation specialists, and patient-specific guidelines for return to prior level of function. The Musculoskeletal Institute at The Johns Hopkins Hospital (a collaboration of orthopedic surgeons, primary care sports medicine physicians, and clinicians from the Department of Physical Medicine and Rehabilitation) presents its rehabilitation protocol with phase-specific guidelines for progression after MPFL reconstruction. This evidence-based protocol is a generalized approach that is customized for each patient's needs.

Sex differences in passive lateral and medial patellar mobility in healthy young adults

BACKGROUND

Sex differences in passive patellar mobility have not been quantitatively evaluated.

OBJECTIVE

The present study aimed to: 1) investigate sex differences in absolute and normalized patellar mobility, and 2) verify the relationship between patellar mobility and knee joint laxity.

METHODS

Two hundred and five pain-free individuals (205 knees, 103 men, 102 women) participated. Passive lateral and medial patellar displacement was measured using a modified patellofemoral arthrometer and manual pushing method at 0∘ and 30∘ knee flexion angles. The absolute values of lateral and medial patellar displacement (LPD and MPD, respectively), and values normalized to patellar width (PW) and body height (HT) were used in the final analysis.

RESULTS

At a 30∘ knee flexion angle, LPD/PW and LPD/HT were greater in women than in men (LPD/PW: 27.0 ± 6.7% vs. 22.6 ± 6.7%, LPD/HT: 0.81 ± 0.19% vs. 0.70 ± 0.15%, respectively, P< 0.001, effect size > 0.50). Absolute and normalized lateral and medial patellar mobility correlated positively with the range of the knee extension angle.

CONCLUSIONS

Sex differences in LPD/PW and LPD/HT at a 30∘ knee flexion were detected in healthy subjects. Although the knee extension angle related to both the lateral and medial direction of the patellar mobility, the relations were only fairly correlated in asymptomatic young subjects.

Femoral articular geometry and patellofemoral stability

BACKGROUND

Patellofemoral instability is a major cause of anterior knee pain. The aim of this study was to examine how the medial and lateral stability of the patellofemoral joint in the normal knee changes with knee flexion and measure its relationship to differences in femoral trochlear geometry.

METHODS

Twelve fresh-frozen cadaveric knees were used. Five components of the quadriceps and the iliotibial band were loaded physiologically with 175N and 30N, respectively. The force required to displace the patella 10mm laterally and medially at 0°, 20°, 30°, 60° and 90° knee flexion was measured. Patellofemoral contact points at these knee flexion angles were marked. The trochlea cartilage geometry at these flexion angles was visualized by Computed Tomography imaging of the femora in air with no overlying tissue. The sulcus, medial and lateral facet angles were measured. The facet angles were measured relative to the posterior condylar datum.

RESULTS

The lateral facet slope decreased progressively with flexion from 23°±3° (mean±S.D.) at 0° to 17±5° at 90°. While the medial facet angle increased progressively from 8°±8° to 36°±9° between 0° and 90°. Patellar lateral stability varied from 96±22N at 0°, to 77±23N at 20°, then to 101±27N at 90° knee flexion. Medial stability varied from 74±20N at 0° to 170±21N at 90°. There were significant correlations between the sulcus angle and the medial facet angle with medial stability (r=0.78, p<0.0001).

CONCLUSIONS

These results provide objective evidence relating the changes of femoral profile geometry with knee flexion to patellofemoral stability.

Investigation of the Relationship Between Flatfoot and Patellar Subluxation in Adolescents

Patellar subluxation is common in adolescents, and a variety of factors are related to this condition, with valgus of the knee joint an important factor. The results of many studies suggest that flatfoot can cause an abnormality of the lower limb power line. Structural abnormalities of the foot caused by the high stresses exerted by body weight can lead to structural deformity of the knee and can also cause knee valgus. Screening for foot problems can help determine the risk of patellar subluxation, and early intervention can lessen the incidence of this condition. The purpose of the present study was to investigate the effects of flatfoot on the structure and function of the knees and, especially, the risk of patellar subluxation. A total of 72 participants were recruited for this cross-sectional study. The mean age at examination was 15.4 ± 4.0 (range 9 to 22) years. The measured parameters were heel valgus angle, arch index, and quadriceps angle (Q-angle). Overall, the mean values of the heel valgus angle, arch index, and Q-angle were 5.9° ± 2.4° (range 1° to 11°), 0.33 ± 0.07 (range 0.23 to 0.46), and 19.1° ± 3.5° (range 9° to 26°), respectively. The Q-angle was directly associated with the heel valgus angle (r = 0.818, p < .001) and arch index (r = 0.655, p < .001). We found that flatfoot can affect the morphology of the knee joint and increase the risk of patellar subluxation.

Acute patellofemoral instability in children and adolescents

Patellofemoral problems are considered to be among the most frequent causes of knee pain in children and adolescents. Correcting bone abnormalities through specific and targeted interventions is mandatory in skeletally immature patients. Medial patellofemoral ligament (MPFL) reconstruction is the preferred procedure, but there are several important precautionary considerations that the surgeon must take into account. It must always be remembered that MPFL rupture is the result, not the cause, of an altered extensor mechanism; therefore, patellar stabilization with MPFL reconstruction is only the first step to be accomplished in the management of an MPFL rupture. If other anatomical alterations are encountered, alternative/additional surgical procedures should be considered. If MPFL rupture occurs without associated anatomical or functional knee alterations, an appropriate rehabilitation program after MPFL reconstruction should be sufficient to achieve a good outcome. In conclusion, an acute patellar dislocation should be managed conservatively unless there is evidence of osteochondral damage or medial retinaculum lesions. Osseous procedures are contraindicated in children, while MPFL anatomical reconstruction with "physeal sparing" is the primary surgical option.

Robot-aided in vitro measurement of patellar stability with consideration to the influence of muscle loading

Background

Anterior knee pain is often associated with patellar maltracking and instability. However, objective measurement of patellar stability under clinical and experimental conditions is difficult, and muscular activity influences the results. In the present study, a new experimental setting for in vitro measurement of patellar stability was developed and the mediolateral force–displacement behavior of the native knee analyzed with special emphasis on patellar tilt and muscle loading.

Methods

In the new experimental setup, two established testing methods were combined: an upright knee simulator for positioning and loading of the knee specimens, and an industry robot for mediolateral patellar displacement. A minimally invasive coupling and force control mechanism enabled unconstrained motion of the patella as well as measurement of patellar motion in all six degrees of freedom via an external ultrasonic motion-tracking system. Lateral and medial patellar displacement were measured on seven fresh-frozen human knee specimens in six flexion angles with varying muscle force levels, muscle force distributions, and displacement forces.

Results

Substantial repeatability was achieved for patellar shift (ICC(3,1) = 0.67) and tilt (ICC(3,1) = 0.75). Patellar lateral and medial shift decreased slightly with increasing flexion angle. Additional measurement of patellar tilt provided interesting insights into the different displacement mechanisms in lateral and medial directions. For lateral displacement, the patella tilted in the same (lateral) direction, and tilted in the opposite direction (again laterally) for medial displacement. With regard to asymmetric muscle loading, a significant influence (p < 0.03, up to 5 mm shift and 8° tilt) was found for lateral displacement and a reasonable relationship between muscle and patellar force, whereas no effect was visible in the medial direction.

Conclusion

The developed experimental setup delivered reproducible results and was found to be an excellent testing method for the in vitro analysis of patellar stability and future investigation of surgical techniques for patellar stabilization and total knee arthroplasty. We demonstrated a significant influence of asymmetric quadriceps loading on patellar stability. In particular, increased force application on the vastus lateralis muscle led to a clear increase of lateral patellar displacement.

The effect of trochlear dysplasia on patellofemoral biomechanics: a cadaveric study with simulated trochlear deformities

BACKGROUND

Trochlear dysplasia appears in different geometrical variations. The Dejour classification is widely used to grade the severity of trochlear dysplasia and to decide on treatment.

PURPOSE

To investigate the effect of trochlear dysplasia on patellofemoral biomechanics and to determine if different types of trochlear dysplasia have different effects on patellofemoral biomechanics.

STUDY DESIGN

Controlled laboratory study.

METHODS

Trochlear dysplasia was simulated in 4 cadaveric knees by replacing the native cadaveric trochlea with different types of custom-made trochlear implants, manufactured with 3-dimensional printing. For each knee, 5 trochlear implants were designed: 1 implant simulated the native trochlea (control condition), and 4 implants simulated 4 types of trochlear dysplasia. The knees were subjected to 3 biomechanical tests: a squat simulation, an open chain extension simulation, and a patellar stability test. The patellofemoral kinematics, contact area, contact pressure, and stability were compared between the control condition (replica implants) and the trochlear dysplastic condition and among the subgroups of trochlear dysplasia.

RESULTS

The patellofemoral joint in the trochlear dysplastic group showed increased internal rotation, lateral tilt, and lateral translation; increased contact pressures; decreased contact areas; and decreased stability when compared with the control group. Within the trochlear dysplastic group, the implants graded as Dejour type D showed the largest deviations for the kinematical parameters, and the implants graded as Dejour types B and D showed the largest deviations for the patellofemoral contact areas and pressures.

CONCLUSION

Patellofemoral kinematics, contact area, contact pressure, and stability are significantly affected by trochlear dysplasia. Of all types of trochlear dysplasia, the models characterized with a pronounced trochlear bump showed the largest deviations in patellofemoral biomechanics.

CLINICAL RELEVANCE

Investigating the relationship between the shape of the trochlea and patellofemoral biomechanics can provide insight into the short-term effects (maltracking, increased pressures, and instability) and long-term effects (osteoarthritis) of different types of trochlear dysplasia. Furthermore, this investigation provides an empirical explanation for better treatment outcomes of trochleoplasty for Dejour types B and D dysplasia.

The effect of tibial tuberosity medialization and lateralization on patellofemoral joint kinematics, contact mechanics, and stability

BACKGROUND

Tibial tuberosity (TT) transfer is a common procedure to treat patellofemoral instability in patients with elevated TT-trochlear groove (TG) distances. However, the effects of TT lateralization or medialization on patellar stability, kinematics, and contact mechanics remain unclear.

HYPOTHESIS

Progressive medialization and lateralization will have increasingly adverse effects on patellofemoral joint kinematics, contact mechanics, and stability.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eight fresh-frozen cadaveric knees were placed on a testing rig, with a fixed femur and tibia mobile through 90° of flexion. Individual quadriceps heads and the iliotibial band were separated and loaded with 205 N in anatomic directions using a weighted pulley system. Patellofemoral contact pressures and patellar tracking were measured at 0°, 10°, 20°, 30°, 60°, and 90° of flexion using pressure-sensitive film behind the patella and an optical tracking system. The intact knee was measured with and without a 10-N patellar lateral displacement load, and recordings were repeated after TT transfer of 5, 10, and 15 mm medially and laterally. Statistical analysis used repeated-measures analysis of variance, Bonferroni post hoc analysis, and Pearson correlations.

RESULTS

Tibial tuberosity lateralization significantly elevated lateral joint contact pressures, increased lateral patellar tracking, and reduced patellar stability (P<.048). There was a significant correlation between mean lateral contact pressure and the TT position (r=0.810, P<.001) at 10°. Tibial tuberosity medialization reduced lateral contact pressures (P<.002) and did not elevate peak medial contact pressures (P>.11).

CONCLUSION

Progressive TT lateralization elevated lateral contact pressures, increased lateral patellar tracking, and reduced patellar stability. Medial contact pressure and tracking did alter with progressive TT medialization, but the changes were smaller.

CLINICAL RELEVANCE

Lateral patellofemoral joint contact pressures increased with progressive lateralization of the TT; medialization of the TT reduced these effects, restoring patellar stability, and did not cause excessive peak pressures. These data provide a rationale for medial TT transfer surgery in patients with elevated TT-TG distances.

MPFL reconstruction: technique and results

Patellar instability is a common problem, and medial patellofemoral ligament (MPFL) injury is inherent with traumatic patellar dislocations. Initial nonoperative management is focused on reconditioning and strengthening the dynamic stabilizers of the patella. For those patients who progress to recurrent instability, further investigation into the predisposing factors is required. MPFL reconstruction is indicated in patients with recurrent instability and insufficient medial restraint due to MPFL injury. A technique of MPFL reconstruction is outlined. This procedure may also be performed in combination with other realignment procedures.

Which patellae are likely to redislocate?

PURPOSE

The purpose of this study was to identify the risk factors for recurrent lateral patellar dislocations and to incorporate those factors into a patellar instability severity score.

METHODS

Sixty-one patients [male/female 35/26; median age 19 years (range 9-51 years)] formed the study group for this investigation. Within the study group, 40 patients experienced a patellar redislocation within 24 months after the primary dislocation, whereas 21 patients, who were assessed after a median follow-up of 37 months (range 24-60 months), had not experienced a subsequent episode of lateral patellar instability. In all patients, age at the time of the primary dislocation, gender, the affected body side, body mass index, bilateral instability, physical activity according to Baecke's questionnaire, the grade of trochlear dysplasia, patellar height, tibial tuberosity-trochlear groove (TT-TG) distance, and patellar tilt were assessed. The odds ratio (OR) of each factor with regard to the patellar redislocation was calculated using contingency tables. Based on these data, a "patellar instability severity score" was calculated.

RESULTS

The patellar instability severity score has six factors: age, bilateral instability, the severity of trochlear dysplasia, patella alta, TT-TG distance, and patellar tilt; the total possible score is seven. Reapplying this score to the study population revealed a median score of 4 points (range 2-7) for those patients with an early episode of patellar redislocation and a median score of 3 points (range 1-6) for those without a redislocation (p=0.0004). The OR for recurrent dislocations was 4.88 (95% CI 1.57-15.17) for the patients who scored 4 or more points when compared with the patients who scored 3 or fewer points (p=0.0064).

CONCLUSION

Based on the individual patient data, the patellar instability severity score allows an initial risk assessment for experiencing a recurrent patellar dislocation and might help differentiate between responders and non-responders to conservative treatment after primary lateral patellar instability.

LEVEL OF EVIDENCE

Case-control study, Level III.

Medial capsule reefing in patellar instability

PURPOSE

The efficacy of medial capsule reefing in the treatment of patellar instability is well documented. Aim of the present study was to prospectively evaluate the outcomes of an all-arthroscopic medial capsule reefing technique in young patients with painful patella syndrome and potential patellar instability.

METHODS

Thirty patients with painful patellar syndrome and potential patellar instability having undergone a minimum of 6 months of intensive rehabilitation were enrolled in the present study. All subjects were evaluated with physical examination, clinical and functional outcomes and complete imaging study.

RESULTS

All patients were reviewed at an intermediate follow-up of 72 months. Average Kujala score improved from 72.9±15.0 to 88.4±7.6 (p<0.0001), average Larsen score from 15.0±2.5 to 17.2±2.2 (p<0.002), average Lysholm from 63.8±16.7 to 87.9±11.7 (p<0.0001) and average Fulkerson score from 69.5±21.5 to 90.8±9.8 (p<0.0001). No intraoperative or postoperative complications were recorded. Ninety per cent of patients were very satisfied or satisfied with their functional result. Twenty-eight patients were reviewed at the final follow-up, 120 months after surgery. Average Kujala was 87.7±8.8 (p<0.0001), average Larsen was 16.8±2.7 (p<0.01), average Lysholm was 87.6±14.3 (p<0.0001), and average Fulkerson was 87.2±13.9 (p<0.0001). Almost 86% of patients were very satisfied or satisfied with their result. However, slight deterioration of the outcomes over time was observed.

CONCLUSION

At the final follow-up, the outcomes of all-arthroscopic technique were significantly improved from preoperative values; however, they were slightly inferior at the 72 months follow-up. This slight deterioration of the outcomes may be the consequence of the reduction in physical activities.

LEVEL OF EVIDENCE

Case series, Level IV.

No difference in patellar tracking between symmetrical and asymmetrical femoral component designs in TKA

PURPOSE

Poor knee extension function after total knee arthroplasty (TKA) is associated with factors including articular geometry and alignment. Femoral trochlear geometry has evolved from symmetrical to become more prominent proximal-laterally, with the groove aligned proximal-lateral to distal-medial. This study in vitro tested the hypothesis that a modern asymmetrical prosthesis would restore patellar tracking and stability to more natural behaviour than an older symmetrical prosthesis.

METHODS

Six knees had their patellar tracking measured optically during active knee extension. Medial-lateral force versus displacement stability was measured at fixed angles of knee flexion. The measurements were repeated after inserting each of the symmetrical and asymmetrical TKAs.

RESULTS

Significant differences of patellar lateral displacement stability, compared to normal, were not found at any angle of knee flexion. The patella tracked medial-laterally within 2.5 mm of the natural path with both TKAs. However, for both TKAs near knee extension, the patella was tilted laterally by approximately 6° and was also flexed approximately 8° more than in the natural knee.

CONCLUSION

The hypothesis was not supported: The more anatomical component design did not provide more anatomical patellar kinematics and stability.

Isolated and combined medial patellofemoral ligament reconstruction in revision surgery for patellofemoral instability: a prospective study

BACKGROUND

Persistent pain and redislocations after surgical treatment of patellofemoral instability are described in up to 40% of patients. However, prospective outcome data about revision surgery are missing.

PURPOSE

To evaluate the clinical outcome after revision medial patellofemoral ligament (MPFL) reconstruction using isolated and combined procedures, with a follow-up of 24 months.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Study participants were 42 patients (median age, 22 years; range, 13-46 years) who underwent revision surgery between January 2007 and December 2009 because of persistent patellofemoral instability after a mean of 1.8 previous failed surgical interventions (lateral release, medial imbrication/vastus medialis obliquus distalization, medialization of the tuberosity). An isolated MPFL reconstruction was performed in 15 cases, while a combination procedure was performed in 27 cases. The clinical results were evaluated preoperatively and 24 months postoperatively using the International Knee Documentation Committee (IKDC), Kujala, and Tegner scores as well as a subjective questionnaire. Patellar shift, tilt, and height, as well as level of degeneration, were defined preoperatively and at the latest follow-up on plain radiographs and magnetic resonance imaging.

RESULTS

At 24-month follow-up, 87% of the patients were satisfied or very satisfied with the treatment. No apprehension or redislocation was reported at follow-up, and there was a significant decrease in pain during daily activities. There were significant improvements (P < .001) in IKDC (from 50 to 80), Kujala (from 51 to 85), and Tegner scores (from 2.4 to 4.9). Patellar shift, tilt, and height decreased significantly (P < .05) to anatomic values, and there was no aggravation to the level of pre-existing degeneration. No significant difference was noticed between the isolated and combined procedures.

CONCLUSION

As patellofemoral instability is a multifactorial problem, revision surgery should be indicated only after a comprehensive examination. The results of this study show that MPFL reconstruction, alone or in combination, seems to be an effective treatment for recurrent patellar dislocations after a failed previous surgery, leading to significant increases in stability and functionality as well as a reduction in pain.

Influence of tibial slope asymmetry on femoral rotation in patients with lateral patellar instability

PURPOSE

The geometry of the tibial plateau and its influence on the biomechanics of the tibiofemoral joint has gained increased significance. However, no quantitative data are available regarding the inclination of the medial and lateral tibial slope in patients with patellar instability. It was therefore the purpose of this study to evaluate tibial slope characteristics in patients with patellar dislocations and to assess the biomechanical effect of medial-to-lateral tibial slope asymmetry on lateral patellar instability.

METHODS

Medial and lateral tibial slope was measured on knee magnetic resonance images in 107 patients and in 83 controls. The medial-to-lateral tibial slope asymmetry was assessed as the intra-individual difference between the medial and lateral tibial plateau inclination considering severity of trochlear dysplasia. The effect of tibial slope asymmetry on femoral rotation was calculated by means of radian measure.

RESULTS

Severity of trochlear dysplasia was significantly associated with an asymmetric inclination of the tibial plateau. Whereas the medial tibial slope showed identical values between controls and study patients (n.s.), lateral tibial plateau inclination becomes flatter with increasing severity of trochlear dysplasia (p < 0.01). Consequently, the intra-individual tibial slope asymmetry increased steadily (p < 0.01) and increased internal femoral rotation in 20° and 90° of knee flexion angles in patients with severe trochlear dysplasia (p < 0.01). In addition, the extreme values of internal femoral rotation were more pronounced in patients with patellar instability, whereas the extreme values of external femoral rotation were more pronounced in control subjects (p = 0.024).

CONCLUSION

Data of this study indicate an association between tibial plateau configuration and internal femoral rotation in patients with lateral patellar instability and underlying trochlear dysplasia. Thereby, medial-to-lateral tibial slope asymmetry increased internal femoral rotation during knee flexion and therefore might aggravate the effect of femoral antetorsion in patients with patellar instability.

LEVEL OF EVIDENCE

III.

A detailed and validated three dimensional dynamic model of the patellofemoral joint

A detailed 3D anatomical model of the patellofemoral joint was developed to study the tracking, force, contact and stability characteristics of the joint. The quadriceps was considered to include six components represented by 15 force vectors. The patellar tendon was modeled using four bundles of viscoelastic tensile elements. Each of the lateral and medial retinaculum was modeled by a three-bundle nonlinear spring. The femur and patella were considered as rigid bodies with their articular cartilage layers represented by an isotropic viscoelastic material. The geometrical and tracking data needed for model simulation, as well as validation of its results, were obtained from an in vivo experiment, involving MR imaging of a normal knee while performing isometric leg press against a constant 140 N force. The model was formulated within the framework of a rigid body spring model and solved using forth-order Runge-Kutta, for knee flexion angles between zero and 50 degrees. Results indicated a good agreement between the model predictions for patellar tracking and the experimental results with RMS deviations of about 2 mm for translations (less than 0.7 mm for patellar mediolateral shift), and 4 degrees for rotations (less than 3 degrees for patellar tilt). The contact pattern predicted by the model was also consistent with the results of the experiment and the literature. The joint contact force increased linearly with progressive knee flexion from 80 N to 210 N. The medial retinaculum experienced a peak force of 18 N at full extension that decreased with knee flexion and disappeared entirely at 20 degrees flexion. Analysis of the patellar time response to the quadriceps contraction suggested that the muscle activation most affected the patellar shift and tilt. These results are consistent with the recent observations in the literature concerning the significance of retinaculum and quadriceps in the patellar stability.

Modern management of patellar instability

Recurrent patellofemoral instability is a disabling condition, attributed to a variety of anatomical aetiologies. Trochlear dysplasia, patella alta, an increased tibial tubercle trochlear groove distance of greater than 20 mm and soft tissue abnormalities such as a torn medial patellofemoral ligament and inadequate vastus medialis obliquus are all factors to be considered. Management of this condition remains difficult and controversial and knowledge of the functional anatomy and biomechanics of the patellofemoral joint, a detailed history and clinical examination, and an accurate patient assessment are all imperative to formulate an appropriate management plan. Surgical treatment is based on the underlying anatomical pathology with an aim to restore normal patellofemoral kinematics. We summarise aspects of assessment, treatment and outcome of patellofemoral instability and propose an algorithm of treatment.

Quadriceps volumes are reduced in people with patellofemoral joint osteoarthritis

OBJECTIVES

This study aimed to (1) compare the volumes of vastus medialis (VM), vastus lateralis (VL), vastus intermedius and rectus femoris and the ratio of VM/VL volumes between asymptomatic controls and patellofemoral joint osteoarthritis (PFJ OA) participants; and (2) assess the relationships between cross-sectional area (CSA) and volumes of the VM and VL in individuals with and without PFJ OA.

METHODS

Twenty-two participants with PFJ OA and 11 controls aged ≥ 40 years were recruited from the community and practitioner referrals. Muscle volumes of individual quadriceps components were measured from thigh magnetic resonance (MR) images. The CSA of the VM and lateralis were measured at 10 equally distributed levels (femoral condyles to lesser femoral trochanter).

RESULTS

PFJ OA individuals had smaller normalized VM (mean difference 0.90 cm(3) · kg(-1), α = 0.011), VL (1.50 cm(3) · kg(-1), α = 0.012) and rectus femoris (0.71 cm(3) · kg(-1), α = 0.009) volumes than controls. No differences in the VM/VL ratio were observed. The CSA at the third level (controls) and fourth level (PFJ OA) above the femoral condyles best predicted VM volume, whereas the VL volume was best predicted by the CSA at the seventh level (controls) and sixth level (PFJ OA) above the femoral condyles.

CONCLUSION

Reduced quadriceps muscle volume was a feature of PFJ OA. Muscle volume could be predicted from CSA measurements at specific levels in PFJ OA patients and controls.

Arthroscopic extraarticular reconstruction of the medial patellofemoral ligament with gracilis tendon autograft - surgical technique

The standard approach to reconstruct the medial patellofemoral ligament (MPFL) is by mini-open incision at its patellar insertion and femoral origin. At the medial patella rim, the MPFL insertion may be visualized in most cases by dissection during surgery. On the femur, it is more difficult to localize the MPFL remnants by a mini-open incision due to soft tissue covering the anatomical origin. Therefore, the femoral MPFL origin is usually identified by intraoperative lateral fluoroscopy. However, the insertion and origin of the MPFL at the patella and femur might be directly visualized using an arthroscopic extraarticular approach from the knee joint through a window of the synovial layer. This is especially helpful on the femoral side but also at the patella to find the individual anatomical MPFL footprints. Arthroscopic extraarticular reconstruction may then be performed using one additional medial mid-parapatellar portal. The major advantages of this technique are an individualized anatomical procedure, which is minimal invasive and cosmetically appealing. The aim of this study was to describe the arthroscopic extraarticular approach to the MPFL insertion at the patella and origin at the femur through synovial windows and to explain the procedure of arthroscopic MPFL reconstruction with a gracilis tendon autograft. Level of evidence Expert opinion, surgical technique, Level V.

Reconstruction of medial patellofemoral ligament for chronic patellar instability

BACKGROUND

Disruption of the capsule, medial patellar retinaculum, and/or vastus medialis obliqus has been associated with recurrent patellar instability. Biomechanical studies have shown that the medial patellofemoral ligament (MPFL) is the main restraint against lateral patella displacement and reconstruction of the MPFL has become an accepted surgical technique to restore patellofemoral stability in patients having recurrent patellar dislocation. We report a prospective series of patients of chronic patellar instability treated by reconstruction of medial patellofemoral ligament.

MATERIALS AND METHODS

Twelve patients (15 knees) with recurrent dislocation of patella, were operated between January 2006 and December 2008. All patients had generalised ligament laxity with none had severe grade of patella alta or trochlear dysplasia. The MPFL was reconstructed with doubled semitendinosus tendon. Patients were followed up with subjective criteria, patellar inclination angle, and Kujala score.

RESULTS

The mean duration of followup after the operative procedures was an average of 42 months (range 24-60 months) 10 knees showed excellent results, 3 knees gave good results, and 2 knees had a fair result. The average patellar inclination angle decreased from 34.3° to 18.6°. The average preoperative Kujala functional score was 44.8 and the average postoperative score was 91.9.

CONCLUSION

MPFL reconstruction using the semitendinosus tendon gives good results in patients with chronic patellar instability without predisposing factors like severe patella alta and high-grade trochlear dysplasia, and for revision cases.

Medial patellofemoral ligament reconstruction with a divergent patellar transverse 2-tunnel technique

BACKGROUND

The medial patellofemoral ligament (MPFL) is the primary passive restraint to lateral patellar dislocation and there is increasing awareness of its role in recurrent lateral patellar instability.

PURPOSE

This study was conducted to prospectively analyze the functional results of a modified MPFL reconstruction technique in recurrent patellar dislocation.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Forty-eight patients (51 knees) with at least 3 episodes of lateral patellar dislocation who had been treated with a 6-month rehabilitation protocol were included in this study. All patients practiced sports regularly. Reconstruction was with a semitendinosus tendon using a divergent 2-tunnel technique. Outcome was evaluated with the Kujala, Larsen, modified Lysholm, and Fulkerson outcome scores. Patient satisfaction with range of motion, pain, and sporting activities was also assessed.

RESULTS

Three patients were lost at the final follow-up, giving a follow-up rate of 94%. The mean follow-up was 33 months. There was no patella dislocation postoperatively. The mean Kujala score improved significantly (P < .01) from 56.7 ± 17.7 (2 × standard deviation) preoperatively to 86.8 ± 14.4 postoperatively. The mean Larsen score improved significantly (P < .01) from 12.4 ± 3.2 to 17.1 ± 2.7. The mean Fulkerson score improved significantly (P < .01) from 59.2 ± 21.8 to 90.1 ± 14. The mean modified Lysholm score improved significantly (P < .01) from 57.6 ± 19.6 to 88.1 ± 16.2. Sixty-four percent of patients returned to the same type of sport at the same level, 16% reduced the level or type of sport for reasons unrelated to the surgery, while 20% reduced the level of sport or changed it for reasons related to surgery. Eighty-seven percent were either satisfied or very satisfied with the pain relief achieved. The patellar tilt decreased significantly from a preoperative mean of 11.1° to 8.9° at the last follow-up (P = .02). The mean preoperative Insall-Salvati ratio of 1.1 decreased to 1.06, although the change was not significant (P = .1).

CONCLUSION

The results of modified MPFL reconstructions are encouraging, with minimal risks of redislocation and an overall patient satisfaction rate of over 80%. These early and medium-term results are comparable with those of other MPFL reconstruction techniques reported in the literature.

What activities do patients with patellar instability perceive makes their patella unstable?

Patellar instability is a disabling musculoskeletal condition. Whilst previous texts have suggested that twisting activities may cause patients to experience instability symptoms, no studies have assessed which activities are related to the patient's perceived instability. The purpose of this study was to determine which activities and with what frequency patients with patellar instability symptoms, perceive their patella to be unstable. Ninety patients referred because of recurrent patellar instability were asked to assess the frequency with which they perceived patellar instability for 19 everyday and sporting activities. The results indicated that sporting and multi-directional twisting activities were more frequently related to patellar instability symptoms, compared to lower energy, uni-planar activities. Females and those without a family history of patellar instability reported more frequent patellar instability symptoms, compared to males, or those with a family history of this disorder. Further study is now recommended to determine whether these results reflect that of patients with milder subluxation disorders, and whether factors such as hypermobility have an impact on perceived patellar instability for this patient group.

The role of trochlear dysplasia in patellofemoral instability

Trochlear dysplasia is characterized by abnormal trochlear morphology and a shallow groove. It is associated with recurrent patellar dislocation, but it is unclear whether the dysplasia is congenital, the result of lateral tracking and chronic instability, or caused by a combination of factors. Lateral radiographs elucidate the crossing sign and characteristic trochlear prominence. Recurrent patellofemoral instability is multifactorial, and each component must be considered in determining treatment. Managing other factors associated with recurrent instability may compensate for a deficient trochlea and provide stability. Medial patellofemoral ligament reconstruction is recommended for patellofemoral instability in the presence of trochlear dysplasia in patients without patella alta or increased tibial tubercle-trochlear groove distance. Trochleoplasty should be reserved for severe dysplasia in which patellofemoral stability cannot otherwise be obtained.

Is latero-medial patellar mobility related to the range of motion of the knee joint after total knee arthroplasty?

Diminished range of motion (ROM) of the knee joint after total knee arthroplasty (TKA) is thought to be related to reduced patellar mobility. This has not been confirmed clinically due to a lack of quantitative methods adequate for measuring patellar mobility. We investigated the relationship between patellar mobility by a reported quantitative method and knee joint ROM after TKA. Forty-nine patients [osteoarthritis--OA: 29 knees; rheumatoid arthritis--RA: 20 knees] were examined after TKA. Respective medial and lateral patellar mobility was measured 1 and 6 months postoperatively using a patellofemoral arthrometer (PFA). Knee joint ROM was also measured in each of those 2 sessions. Although the flexion and extension of the knee joints improved significantly from 1 to 6 months after TKA, the medial and lateral patellar displacements (LPDs) failed to improve during that same period. Moreover, only the changes in knee flexion and medial patellar displacement (MPD) between the two sessions were positively correlated (r = 0.31, p < 0.05). However, our findings demonstrated that medial and lateral patellar mobility had no sufficient longitudinal relationship with knee ROM after TKA.