Once MPS is suspected after a thorough history and physical examination, examination under anesthesia accompanied by diagnostic arthroscopy confirms the diagnosis. Lateral forces are applied to the patella in full knee extension and 30° of flexion (Figure 3). During arthroscopy, the patellofemoral compartment is viewed from the anterolateral portal. With the knee at full extension, the lateral laxity and medial tilt of the patella can be identified (Figure 4). As the knee is flexed to 30°, the patella moves medially and can subluxate over the edge of the medial facet of the trochlea (Figure 5).
Treatment
Nonsurgical Management
Treatment of MPS depends entirely on making an accurate diagnosis and determining the degree of impairment. Patients with symptomatic MPS should initially undergo supervised rehabilitation focusing on balancing the medial and lateral forces that influence patellar tracking. Patients should be evaluated for specific muscle tightness, weakness, and biomechanical abnormalities. Each problem should be addressed with an individualized rehabilitation prescription. Emphasis is placed on balance, proprioception, and strengthening of the quadriceps, hip abductors/external rotators, and abdominal core muscle groups.
In some patients, symptomatic MPS may be reduced with a patella-stabilizing brace with a medial buttress.3,5,26 Although bracing should be regarded as an adjuvant to a structured physical therapy program, it can also be helpful in confirming the diagnosis of MPS. Shannon and Keene3 reported that all patients in their study experienced significant pain relief and decreased medial patellar subluxations when they wore a medial patella–stabilizing brace. Shellock and colleagues25 used kinematic MRI to investigate the effect of a patella-realignment brace and found that bracing counteracted patellar subluxation in the majority of knees studied.
Surgical Management
When conservative management fails and patients continue to experience pain and instability, surgical intervention is often required. Although various surgical techniques have been used (Table),3–6,8–10,14,15,27,28 the optimal surgical treatment for MPS has not been identified.
Lateral Retinaculum Imbrication. Lateral retinaculum imbrication has been used to centralize patella tracking and stabilize the patella. Richman and Scheller5 reported on a 17-year-old patient who had isolated medial subluxation of the patella without having undergone a previous lateral release. At 3-month follow-up, there was no recurrent instability; there was only intermittent medial knee soreness with weight-bearing activity.
Lateral Retinaculum Repair/Reconstruction. Hughston and colleagues8 treated 65 knees for MPS. Most had undergone lateral release. Of the 65 knees, 39 were treated with direct repair of the lateral retinaculum, and 26 with reconstruction of the lateral patellotibial ligament using locally available tissue, such as strips of iliotibial band or patellar tendon. Results were good to excellent in 80% of patients at a mean follow-up of 53.7 months. Nonweiler and DeLee6 reconstructed the lateral retinaculum in 5 patients with MPS that developed after isolated lateral retinacular release. Four (80%) of the 5 patients had no symptoms or physical signs of instability at a mean follow-up of 3.3 years. Results were excellent (3 knees) and good (2 knees) according to the Merchant and Mercer rating scale. Akşahin and colleagues28 reported on a single case of spontaneous medial patellar instability. At surgery, imbrication of the lateral structures failed to prevent the medial subluxation. Lateral patellotibial ligament augmentation was performed using an iliotibial band flap that effectively corrected the instability. At 1 year, the patient was characterized as engaging in vigorous recreational activity, according to the clinical score defined by Hughston and colleagues.8 He had mild pain with competitive sports but no pain with daily activity. Abhaykumar and Craig9 reported on 4 surgically treated knees with medial instability. They reconstructed the lateral retinaculum using a strip of fascia lata. By follow-up (5-7 years), each knee had its instability resolved and full ROM restored. Johnson and Wakeley26 reported on a case of iatrogenic MPS after lateral release. Treatment consisted of mobilization and direct repair of the lateral retinaculum. At 12-month follow-up, there was no instability. Although symptom-free with light activity, the patient had patellofemoral pain with strenuous activity. Sanchis-Alfonso and colleagues14 reported the results of isolated lateral retinacular reconstruction for iatrogenic MPS in 17 patients. At mean follow-up of 56 months, results were good or excellent in 65% of patients, and the Lysholm score improved from 36.4 preoperatively to 86.1 postoperatively.
Medial Retinaculum Release. Medial retinaculum release has been used as an alternative to open reconstruction. Shannon and Keene3 reported the results of medial retinacular release procedures on 9 knees. Four (44%) of the 9 patients had either spontaneous or traumatic onset of instability. All cases were treated with arthroscopic medial retinacular release, extending 2 cm medial to the superior pole of the patella down to the anteromedial portal. This avoided releasing the attachment of the vastus medialis oblique muscle to the patella and removing its dynamic medial stabilizing force. At a mean follow-up of 2.7 years, both medial subluxation and knee pain were relieved in all 9 knees without complications or further realignment surgery. Results were excellent in 6 knees (66.7%) and good in 3 knees (33.3%). Shannon and Keene3 emphasized that the procedure should not be used in patients with hypermobile patellae or in cases of failed lateral retinacular releases in which MPS is not clearly and carefully documented.