Abstract
Objectives:
Habitual and fixed patellar dislocations represent extreme forms of patellar instability and can lead to significant functional loss. The underlying complex pathoanatomy of a laterally positioned and shortened extensor mechanism pose challenges in its management. The first purpose of the study was to evaluate the presence of these anatomic risk factors in habitual and fixed patellar dislocations. Conservative treatment options including bracing, physical therapy and activity modifications are not sufficient to correct or compensate for the underlying pathoanatomy of habitual and fixed dislocations. Since the primary pathology is a laterally positioned, externally rotated and shortened quadriceps mechanism, the cornerstone of treatment is an anterior repositioning and lengthening of the quadriceps mechanism, known as a quadricepsplasty. The second purpose of our study was to evaluate the clinical outcomes of a 4-in-1 quadricepsplasty (wide lateral releases, Insall’s proximal tube realignment, Roux- Goldthwait patellar tendon hemi-transfer, step-wise quadriceps lengthening) for stabilization of habitual and fixed patellar dislocation.
Methods:
In a retrospective study, all patients with habitual and fixed patellar dislocation who underwent a 4-in-1 quadricepsplasty and had minimum 2 year follow-up, were identified. Preoperative MRIs were evaluated for the presence of anatomic risk factors. Trochlear dysplasia was determined based on trochlear depth measurements on axial MRI, and trochlear depth < 3 mm was considered abnormal. Patellar height was calculated using the Caton-Deschamps index on sagittal section; >1.2 was considered to be abnormal. Tibial tubercle lateralization was calculated based on Tibial Tubercle to Trochlear groove distance (TTTG) distance on axial MRI; >20 mm was considered pathologic. Lateral patellar tilt was defined as the angle between the widest portion of the patella and a line tangential to the posterior surface of the femoral condyles on axial view and tilt > 20° was considered abnormal. The prescence of any effusion, bone bruises, osteochondral fracture, or chondral lesions were also noted.
The procedure is performed through a single 15 cm midline knee incision. Wide lateral releases and lateral arthrotomy are performed after release of all tethers to the lateral aspect of the patella including subcutaneous tissues, iliotibial band, lateral retinaculum, and vastus lateralis tendon. The lateral retinaculum is cut in a coronal Z-fashion to achieve retinacular lengthening at the time of closure. A medial arthrotomy is performed and the patella is repositioned on the trochlea. Next, the Roux- Goldthwait procedure is performed by medial transposition of lateral half of the patellar tendon. Then the medial flap of medial arthrotomy which includes the vastus medialis muscle and the medial retinaculum is brought over the patella and sutured to its lateral aspect enclosing the patella in a quadriceps ‘tube’. The medial parapatellar arthrotomy is the modification of Insall’s ‘tube’ realignment procedure. Finally, the quadriceps mechanism is sequentially lengthened. The knee is flexed to 90° and vastus lateralis tendon is sutured to the side of quadriceps tendon. The new site of vastus lateralis attachment is more proximal compared to its normal insertion; this lengthens the lateral aspect of quadriceps mechanism. A formal Z-lengthening of quadriceps tendon is seldom required and is performed if 90° knee flexion could not be achieved with the patella repositioned. Postoperatively, a long leg cast is applied for 3-4 weeks.
Operative notes were reviewed to collect detailed information related to the procedure. Postoperative course, including complications, were noted. Patient reported outcomes were collected using validated instruments including Pedi-IKDC, HSS-Pedi FABS activity score, Banff Patellar Instability Index (BPII) Kujala score and KOOS score.
Results:
17 knees (12 patients) formed the study cohort. 12 knees had habitual dislocation and 5 had fixed dislocation. Mean age was 9.7 years. 6/17 (35.3%) knees were associated with syndromes. On MRI, trochlear dysplasia was the most common anatomic risk factor present in 15/17 (88.2%) knees. 13/17 (76%) knees had presence of 2 or more risk factors. At mean follow-up of 39.3 months, the mean Pedi-IKDC score was 88.1, HSS Pedi-FABS activity score was 15.6, BPII score was 78.2, Kujala score was 90, KOOS score was 93.9, and overall patient satisfaction score was 83.3. For complications, 3/17 knees (17.6%) had recurrent patellar instability, 1 knee had postoperative stiffness that required manipulation under anesthesia and one knee had a superficial wound infection.
Conclusions:
Most patients with habitual and fixed patellar dislocation present during the first decade of life. There are several underlying anatomic risk factors, the most common being trochlear dysplasia and patellar tilt. The 4-in-1 quadricepsplasty technique provides reliable patellar stabilization, satisfactory clinical results and acceptable patient reported outcomes at minimum two-year follow-up, with 17.6% re-dislocation rate. Our results, including redislocation rates and patient-reported outcomes are comparable to previously published studies. We prefer to detach the vastus lateralis tendon from its insertion on to the patella / quadriceps tendon and then reattaching it to the quadriceps tendon in a proximal position once the patella is centered in the trochlear groove and with the knee bent to 90°.
This would avoid proximal detachment of entire vastus lateralis muscle and decrease the morbidity related to it. The other advantages of our technique is that it is a physeal respecting procedure and can be performed in limited resource set-up as there is no routine need for implants, arthroscopy, fluoroscopy or drilling.
