Medial patellar instability (MPI) is a debilitating condition most associated with previous lateral-sided procedures1-3. Several studies cite rates of iatrogenic MPI (IMPI) over 50% in patients with previous lateral retinacular release (LRR)2,4,5. Patients with MPI complain of unrelenting patellofemoral pain and instability6,7. Many are unable to work and disability is pervasive8,9. Underlying hyperlaxity, trochlear dysplasia, or deficient vastus lateralis musculature can also play a significant role in MPI1,10. Diagnosis relies on careful physical examination, with several proven ancillary examinations when MPI is suspected7,11-16.
In patients with connective tissue disorders that manifest in hyperlaxity, MPI is especially problematic. Ehlers-Danlos syndrome (EDS) is a disorder resulting from abnormal collagen function and composition17. The existing EDS literature reveals it to be difficult to diagnose, and prone to higher failure rates in surgical managment18.
The patient was informed that data concerning the case would be submitted for publication, and she provided consent.
We present a case where bilateral medial and lateral patellofemoral ligament (MPFL, LPFL) reconstruction successfully treated MPI in a 35-year-old woman with EDS hypermobility type, diagnosed by meeting all criteria for the disease and including Beighton score. No genetic testing for hypermobility type EDS is currently available in the United States19. The patient came to our clinic, 3-year status after bilateral complete arthroscopic LRR's, complaining of right knee MPI and 10/10 debilitating pain. Medial dislocations were occurring daily, with increasing frequency; less often, lateral dislocations also occurred. Physical examination of the knee revealed only 4° hyperextension and 125° flexion due to pain and effusion. There was 3+ quadrant patellar mobility medially and 1+ quadrant laterally (Figs. 1-A, 1-B, and 1-C). No computed tomography or other cross sectioning imaging was obtained to measure tibial tubercle (TT) to trochlear groove distance, as the patella tracked midline, the TT was not lateralized, and TT transfer would alter patellofemoral contact pressures. The remaining examination was benign and the extremity was neurovascularly intact. Plain film radiographs of the right knee showed no trochlea dysplasia (sulcus angle 134°) and expected abnormal lateral patella tilt of approximately 6.5° (Fig. 2). Given the frequent dislocations and decrease in quality of life, we made the decision to proceed with MPFL and LPFL reconstruction of the right knee.
Preoperative right knee at rest (Fig. 1-A), with lateral patellar stress (Fig. 1-B), and with medial patellar stress (Fig. 1-C).
Using a technique described by Saper and Shneider, reconstruction began with examination under anesthesia, showing 3+ quadrant medial and 1+ quadrant lateral patellar subluxation at both full extension and 30° flexion20. A diagnostic arthroscopy was performed, pertinent positives of which were wear on the articular surface of the medial and lateral patellar facets and softening of cartilage on the medial femoral condyle. Patella tracking was viewed from 0° to 30° flexion through inferior and superior portals and found to be midline. The scope was withdrawn, the knee drained of excess fluid, and a midline longitudinal incision superior to the patella was made and full-thickness flaps elevated. A recent anatomic study has shown that the quadriceps tendon has a trilaminar structure to it, created from 6 quadriceps muscle contributors21. The plane of the intermediate layer was exploited with small, longitudinal incisions in the medial and lateral aspects of the tendon, and sharply creating a transverse tunnel just proximal to the superior pole of the patella, which we marked with a #2 FiberLoop (Arthrex). Using fluoroscopy and an Arthrex radiographic guide (Arthrex), the origin of the MPFL at Schottle point was identified and marked on the skin (Fig. 3). A stab incision was made and blunt dissection carried down to Schottle point22. When trajectory was confirmed with C arm, a 2.4-mm guidewire was inserted then over-reamed with a cannulated 4.5-mm reamer to 25-mm depth. We took our semitendinosus allograft, 5 mm in diameter, previously prepared with #2 FiberWire (Arthrex) whipstitching, and seated one end into the femoral tunnel utilizing a 4.75-mm Arthrex BioComposite SwiveLock anchor (Arthrex). Alternatively, an interference screw may be used, the difference being that the anchor provides 3 sides of fixation and a stronger construct versus the 2 sides of a screw due to eyelet pull through of the graft in the screw23. We then tunneled the graft from the MPFL origin subfascially up to our quadriceps tunnel and gently through to the lateral side. The structure of the quadriceps tendon holds the allograft securely, negating the need for suture attachment. Under fluoroscopic guidance, origin of the LPFL was marked on the skin at a point slightly distal and anterior to the lateral epicondyle24. A stab incision was made, the iliotibial band incised, and blunt dissection carried down to the femur. Once trajectory was confirmed with C-arm in the anterior to posterior and lateral planes, a 2.4-mm guidewire was inserted, and over-reamed with a 4.5-mm reamer to 25 mm (Fig. 4). We passed our graft from the lateral aspect of the quadriceps tunnel subfascially to the LPFL origin. The knee was placed into 60° flexion and a towel clamp was used to place a superior longitudinal force on the patella to simulate quadriceps contraction. We gently held tension on the graft to avoid over-tensioning with extension, marked the graft where it would insert into the femoral tunnel, transected excess graft, and seated it with a 4.75-mm anchor. Medial and lateral translations of the patella at 0° and 30° were found to have firm endpoints and no excess translation. We then confirmed the knee could be flexed to 90° without undue tension on the extensor mechanism. The fascial and skin incisions were carefully closed given the patient's EDS, finishing with a running subcuticular 4-0 Monocryl. An overall schematic is shown (Fig. 5). The patient was placed in a hinged knee brace locked in extension, admitted overnight for observation, and discharged the following day.
The patient was placed on aspirin for deep venous thrombosis prophylaxis and entered our 6- to 9-month MPFL reconstruction protocol. She was seen regularly for 2 years. Her brace was discontinued at week 10 in favor of a patellar stabilizing orthosis. At 1-year follow-up of the right knee, the patient was so pleased with the results she requested the same procedure for the left knee, where MPI had become disabling. We complied after physical examination revealed substantial MPI, and reconstructed the left MPFL and LPFL in the exact manner described above. At 2-year follow-up of the right knee, the patient had experienced no further dislocation events, and there was no patellar hypermobility on physical examination (Figs. 6-A, 6-B, and 6-C); she was brace free, rated knee pain as 0/10, and had a knee injury and osteoarthritis outcome score (KOOS) symptoms subscale score of 67.9. Radiographs showed improved patellar tilt, midline positioning, and no patella alta (Figs. 7-A and 7-B).
Postoperative right knee at rest (Fig. 6-A), with lateral patellar stress (Fig. 6-B), and with medial patellar stress (Fig. 6-C).
Right knee postoperative x-rays at 2-year follow-up showing sustained midline patellar alignment with improved patellar tilt of 3.4° (Fig. 7-A), and normal sulcus angle (Fig. 7-B). Insall-Salvati ratio within normal limits of approximately 0.86.
Patellofemoral instability rates are as high as 57% among patients with EDS25,26. Hughston and Deese first reported on IMPI, finding it in 50% of knees that had undergone LRR27,28. In a systematic review of IMPI after LRR, Song et al. found 57% of 300 knees exhibited IMPI4. They found statistically significant relationships between IMPI and preoperative tightness of the lateral retinaculum, extent of LRR, and over-release of the lateral retinaculum and vastus lateralis4. In a 2007 study of arthroscopic medial retinacular release, of the 154 cases of MPI reported in the literature to that date, 94% had undergone a previous LRR29. The existing literature contains a single review of the results of surgical intervention for IMPI30. The review covers 8 studies involving 201 knees, and 6 different surgical techniques: reconstruction of the lateral retinaculum, direct repair of the lateral retinaculum, LPFL reconstruction, lateral patellotibial ligament reconstruction, arthroscopic medial retinacular release, and fascia lata sling reconstruction. Although the majority of these studies reported good to excellent outcomes and high patient satisfaction, the review underscores the need for high-powered studies of IMPI.
There is one case report of simultaneous reconstruction of the MPFL and LPFL, where hamstring autografts were double bundled and placed into shared patellar bone tunnels31. Although the patient reported improvement in pain and instability, medial instability remained, attributed to a previous Roux-Goldthwait procedure. Otherwise, the technique presented here and pioneered by Saper and Shneider is the only published technique of simultaneous reconstruction.
EDS is an underdiagnosed condition, and before diagnosis, many patients with EDS will have undergone multiple orthopaedic procedures with poor results32-36. Additionally, patellar instability in patients with EDS can lead to premature patellofemoral arthritis, higher incidence of meniscal and ligament injury, and chronic knee pain rates of 85% to 100%10,37,38.
Although this procedure would likely have been performed in any person presenting with our patient's constellation of symptoms and rapidly deteriorating quality of life, in patients with EDS with knee pain, suspicion for MPI should be heightened. When previous LRR has been performed, MPI should be ruled out. We believe our case presents an effective long-term technique for restoring medial patellar stability while minimizing use of the pathologic EDS tissue, and with relatively low morbidity, immediate postop rehab, and no risk of patella fracture. Further high-powered studies concerning the outcomes of surgically treated MPI are warranted.
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