PATELLAR DISLOCATIONS

DAVID J. ABRAHAM, MD Resident Orthopaedic Surgery

FREEMAN MILLER, M.D. Attending Pediatric Orthopaedic Surgeon

May 7, 1996

CLINICAL CASE PRESENTATION

ORTHOPAEDIC DEPARTMENT

THE ALFRED I. DUPONT INSTITUTE

WILMINGTON, DELAWARE

CASE HISTORY:

A 16 year old 220 pound black male was evaluated at the Sports Medicine Clinic at AIDI 6 days after sustaining an acute injury to his right knee while playing baseball. The patient related that he noticed acute onset of R knee after striking out at bat. He heard a single clunk in his knee and noticed immediate pain and swelling. He was evaluated at a local emergency department and placed into a knee immobilizer and told to follow up in Sports Medicine. He noticed that the knee "gave out" on him several times since the accident.

On physical exam of the patient six days after injury the knee was noted to have a large effusion. ROM was limited from 20 to 100 degrees of flexion. There was significant medial retinacular tenderness with a mildly positive apprehension test. His ACL, PCL, MCL and LCL ligaments were intact. McMurry's test was negative, and his Q angle was 15 degrees.

Radiographs revealed a large medial femoral defect and an intraarticular calcification. Based on these radiographs and his mechanical symptoms surgery was performed for arthroscopic loose body excision. At arthroscopy the medial femoral condylar defect was not apparent, but a large retinacular tear was discovered. Also, the patient had an osteochondral fracture of the lateral femoral condyle and a free 7mm by 5mm intraarticular cartilage fragment which was removed.

PATELLAR DISLOCATIONS:

• Most commonly due to twisting injury to knee.
• Only 10 % caused by direct trauma
• 24% incidence of positive family history of patellar dislocation
• Risk factors include:

1. Shallow patellofemoral articular groove
2. Patella alta
3. Excessive Q angle
4. Generalized ligamentous laxity

• Average age is 16- 20 years old, rare over 30
• Most common sports are football, basketball, baseball but not unusual in gymnastics, simple falls, cheerleading or dancing.
• Female sex often associated with increased incidence of patellar dislocation

EVALUATION:

• Patient presents with a large, swollen knee held in a flexed position with a prominent medial femoral condyle
• Reduced by gentle extension of the tibia, forceful medial pressure on the patella is avoided. Often helpful to place the patient in the prone position to extend the hip and relax the hamstrings.
• After reduction the patient has diffuse parapatellar tenderness and often a palpable medial retinacular defect (vastus medialis insertion)
• Hemarthrosis can develop from the capsular tear and/or an osteochondral fracture (usually the lateral femoral condyle or medial patella)
• Pre-reduction XR will often miss the OCD, bone fragments along the medial patellar margin may be an avulsion fracture of the vastus insertion.

NONOPERATIVE TREATMENT:

• After reduction aspiration should be considered for a tense hemarthrosis, blood checked for fat droplets indicating OCD
• Knee is placed in a knee immobilizer with lateral patellar pad to hold patella in a reduced position Quad strengthening started as soon as possible with straight leg raising.
• Natural history of nonoperativly treated patellar dislocations involve recurrance in 1 in 6, minor residual symptoms in 2 of 6, and 3 of 6 will be asymptomatic.(McManus, 1979.)
• The incidence of recurrant dislocation is decreases with age (Cash and Hughston, 1987.)

14 year olds 60% redislocation

17-28 year olds 30 % redislocation

greater than 28 rare

OPERATIVE TREATMENT:

• Consider surgery for patients at high risk for recurrant dislocation:
• Risk factors:
1. Osteochondral fracture of lateral femoral condyle
2. age less than 14
3. highly active/competative athlete
4. palpable medial vastus defect
5. contralateral evidence of dysplasia
6. family history
7. patella alta
• The role of lateral release in the treatment of recurrant dislocation is controversial
• Metcalf reviewed 14 patients with recurrant dislocation and found 9 good, and 3 excellent results with 0 incidence of medial instability after arthroscopic lateral release.
• Some feel that patients with obvious medial defect benefit from open advancement of medial retinaculum and lateral release
• Patients with increased Q angle and ligament laxity may benefit from distal realignment
• Roux-Goldthwait procedure involves splitting the patellar tendon and medializing the lateral half (93% success)
• Hauser procedure transfers the patellar tendon and bony block of tibia medially. (increased risk of developing OA secondary to increased joint contact forces.)
• Elmslie Trillot Procedure-medially rotation a segment of ant. tibial cortex including tibial tubercle

REFERENCES:

1. Cash JD, Hughston JC. Treatment of acute patellar dislocation. Am J Sports Med 1988; 16, 244.
2. Larsen E. Conservative treatment of patellar dislocations. Clin Orthop 1982, 171:1321.
3. McManus F, Rang M, Ahislin DJ. Acute dislocation of the patella in children: the natural history. Clin Orthop 1979; 139, 88.
4. Metcalf RW. An arthroscopic method of lateral release of the subluxating or dislocating patella. Clin Orthop 1982: 167, 9.