Patellar Dislocation Treatment Options
Many dislocations will reduce on their own but some will require reduction. This is attempted many times in the field or on the sidelines during sporting events, but some may require sedation. This is generally performed by placing medial pressure on the patella while extending the knee. Patellar dislocations can lead to cartilage injuries, osteochondral fractures, recurrent instability, chronic pain and patellar osteoarthritis. As with shoulder dislocations, recurrence is not uncommon. Reports range from 15% to 80 % and after a second dislocation, the chance of patellar instability is greater than 50 percent [1-4]. A heterogeneous patient population, challenging surgical techniques and lack of long-term and robust clinical outcome studies make the management of recurrent patellar instability very difficult.
The first thing once reduction is confirmed is determine is whether or not this is the first occurrence. The provider will need to take a thorough history as dislocations may be subtle or difficult to determine on some occasions. Reduction can sometimes occur if an athlete is rolling on the ground or when the patient is getting up. It is important to ask about knee effusion or one of multiple acute “pop” or “cracks.” Some providers will order advanced imaging on patients after a patellar dislocation to ensure there is no osteochondral fracture or acute osteochondral defect, nondisplaced fracture or large cartilage defects of the patella or femur. Following acute injury, MRI can detect characteristic findings of a patellar dislocation, including cartilage damage that may be undetected on radiographs or bone bruising on the medial patellar facet and the lateral femoral condyle [5,6]. Standard MRI was compared with intraoperative findings and was found to be 85% sensitive and 70% accurate in detecting injury to the MPFL [7]. Concomitant cartilage injuries to the patellofemoral joint can be expected in 70% to 96% of knees with both acute and recurrent patellar dislocations [8].
Image 1. Xray demonstrating laterally dislocated patella (courtesy of wikipedia)
High-level evidence supports nonoperative management of first time dislocations if there are no large cartilage defects, loose bodies or intra-articular damage [9,13]. There is debate and studies with better short term results and lower chance of dislocation with surgical management, but long term studies have shown equal clinical outcomes. A brief period of immobilization with crutches, protected weight bearing may be used for comfort the first week. Some providers may choose to aspirate a large or tense effusion. Hinged knee braces or lateral stabilization braces along may be used along with physical therapy. Bracing may enhance the patient’s sense of stability [10-11]. Approach includes gradual increase in controlled motion followed by or paired with an emphasis on strengthening. This includes core, hip and quadriceps strengthening, balance/proprioception exercises and closed chain quadriceps exercises. Patients should be informed of redislocation risk, especially if athletes are returning to sport within 3-6 weeks. Atkin et al. reviewed results of 74 patients (37 males and 38 females) at six months after nonoperative management and noted that, following an initial patellar dislocation, 58% of patients continued to have limitations with strenuous activity (usually kneeling or squatting) and 55% had not returned to sports [12]. A randomized trial by Palmu et al. with 71 patients showed good or excellent outcomes for 75% of nonoperatively treated knees and 66% of operatively treated knees. The rates of dislocation were similar. [9]
As mentioned earlier, there is a high rate of soft tissue injury with patellar dislocations. If a displaced osteochondral fracture or loose body occurs, some orthopedic surgeons may perform an arthroscopic removal or repair of the osteochondral fragment. There is no definitive cut off, but some use 15 mm as a cut off for the size of the lesion or loose body [9]. Another indication for some providers includes a bony avulsion of the medial patellofemoral ligament. A systematic review of four overlapping meta-analyses by Erickson et al. found that operative treatment of acute patellar dislocations may result in a lower rate of recurrent dislocations than non-operative treatment (24.0% vs. 34.6%), but did not improve functional outcome scores [14].
Image 2. Illustration of normal patella, patellar subluxation vs patellar dislocation (courtesy of kneeandshoulderclinic.com.au)
The incidence of recurrent patellar instability after conservative treatment ranges from 15% to 40% of cases [15]. The risk of redislocation increases by 6 times in patients with a history of contralateral patellar dislocation. If two dislocations occur, the risk of redislocation has been reported to be up to 50% or even higher if the MPFL is injured [16]. Recently, algorithms and guidelines are being proposed depending on risk factors and imaging of patients with recurrent dislocators. If there is an MPFL ligament that is partially or fully torn, an MPFL reconstruction may be done. Some orthopedic surgeons use grafts and many techniques exist. Techniques differ with graft choice, graft positioning, graft tension and there is a paucity of clinical comparative studies. Many surgeons and groups now advocate for a more anatomic approach with the femoral tunnel. A recent systematic review noted an overall complication rate of 26.1% in patients from six to fifty-five years old (average, twenty-four years). The most common adverse events included recurrent apprehension, arthrofibrosis, pain and clinical failure, and patellar fracture [17]. Despite the numerous associated complications, most clinical studies have described retrospective data with 80% to 96% of the patients having a good or excellent clinical outcome [18,19].
One study in 143 patients with recurrent instability showed 85 percent had trochlear dysplasia, which sparked new clinical trials with trochleoplasty. Indications for trochleoplasty include aberrant patellar tracking (identified by a J sign on clinical examination and a TT-TG distance of >10 mm) and abnormal trochlear morphology (identified on a true lateral radiograph as overlap of the posterior condyles or on an axial MRI or CT scan) [21]. The technical considerations for a deepening trochleoplasty include elevating a strip of cortical bone adjacent to the trochlea in order to remove underlying cancellous trochlear bone, thus deepening the trochlear groove, before reapproximating the overlying healthy bone and cartilage. Complications specific to the procedure include iatrogenic cartilage damage, patellar incongruence, overcorrection, arthrofibrosis, and advanced arthrosis [20-22]. Given the technical demands and potential complications, it is not surprising that the clinical outcomes following trochleoplasty for recurrent instability are mixed, with satisfaction ratings ranging from 67% to 95.7% [20-24]. Currently, trochleoplasty should be reserved for surgeons with vast experience with these techniques and for patients with recurrent and complex patellofemoral instability.
Medial tibial tubercle transfer (Elmslie-Trillat procedure) and anteromedialization of the tibial tubercle (Fulkerson procedure) have been described to alter osseous alignment in the setting of recurrent patellar instability [25-30]. These techniques involve cutting or altering the tibial tubercle and fixing the bone to a new location depending on the procedure. Patella alta and abnormal patellar tracking secondary to external tibial torsion relative to the trochlear groove are typically addressed. The selected plane of the osteotomy needs to be individualized for each patient. A modified Elmslie-Trillat procedure in a 15 to 20 plane that medializes and corrects malrotation may be the most frequently used approach for patients with typical recurrent instability. The indications for a distal realignment in the setting of recurrent instability include a TT-TG distance of >15 mm and a Caton-Deschamps ratio of >1.4 [31-33]. Isolated medialization of the tibial tubercle decreases the resultant lateral force vector acting on the patella and consequently increases patellofemoral stability. The preferred magnitude of medialization varies, but the majority of researchers agree that postoperative TT-TG goals should be 9 to 15 mm [34-35]. Anteromedialization is another approach that combines the positive effects of the isolated medial and anterior transfers. A long osteotomy is performed to maximize the surface area and provide sufficient length for safe fixation with a minimum of two screws to control both rotation and translation [37]. The approach is individualized to balance correction of the malrotation against the potential impacts of patellofemoral contact mechanics and chondral surfaces. The overall complication rate following osseous distal realignment procedures has been reported to be 7.4 percent, with more than 50 percent being from symptomatic hardware [37-38]. Procedures alongside tibial tubercle transfer such as lateral release, MPFL reconstruction and trochleoplasty are common. Limitations exist in the literature, but there is a low chance of redislocation (0 to 15 percent) and satisfaction rates of good or excellent were 63 to 90 percent [38-39].
Variations of soft tissue procedures including a lateral release and/or medial reefing were commonly used in the absence of bony deformity over the last three decades to achieve proximal realignment. Lateral release involves cutting the retinaculum, the joint capsule and synovial tissue longitudinally as far as the distal fibers of the vastus lateralis, approximately 2 cm proximal to the superior patellar pole and reefing is a procedure to abrade the synovial membrane and capsule to stimulate bleeding. Several studies have demonstrated that an isolated lateral release is associated with high rates of recurrent dislocations and poor clinical outcomes [40-41]. On the other hand, the combination of lateral release with medial soft tissue reefing, appeared to lead to a decrease in recurrent instability rates and an increase of patient satisfaction [42]. Arthroscopic lateral release is only effective in patients with a positive lateral tilt (i.e., a tight lateral retinaculum) who have failed exhaustive conservative measures. However, a lateral release should not be used to treat patellar instability or the patient with generalized ligamentous laxity and its associated patellar hypermobility. A common complication of this procedure incorrectly used for the patient with patellar instability rather than a tight lateral retinaculum is iatrogenic medial patellar subluxation or worsened instability [43].
One final procedure described will be the derotational osteotomy. Unrecognized excessive femoral anteversion alters the forces across the patellofemoral joint, with a greater laterally directed force vector. If rotational malalignment is suspected, advanced imaging with CT or MRI should be performed to quantify the deformity [46]. Derotational osteotomy for excessive femoral anteversion (an anteversion of >20) should be performed in patients with failed soft-tissue procedures or if all contributing osseous and soft-tissue factors are to be addressed concomitantly. It may be done proximally in the intertrochanteric region or distally in the supracondylar region with both options yielding good-to-excellent results [44-45].
Figure 1. Treatment algorithm for recurrent patellar instability (adopted from Weber, 2016)
In summary, treatment needs to be individualized and depends on many factors. Many groups recommend non-operative treatment for first time dislocations without any large osteochondral defects or loose bodies. For recurrent dislocations or patellar instability, many techniques are described and techniques are combined in many cases. There are algorithms proposed for certain risk factors and radiologic findings. Most surgeries are technically challenging and needs to be performed by providers with proper training and experience.
– More Knee Pain from Sports Medicine Review: https://www.sportsmedreview.com/by-joint/knee/
– Read More: https://wikism.org/Patellar_Dislocation
– https://www.sportsmedreview.com/blog/patellar-dislocation-introduction-and-diagnosis
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