Non-operative Management of Traumatic Patellar Dislocation: Analysis of risk factors and cartilage deterioration

The main objective of this dissertation was to fill a few knowledge gaps along the natural course of the concept of patellar dislocation. In Study I of this dissertation, we investigated whether patients with bilateral recurrent patellar dislocation have bilaterally greater femoral anteversion than patients without the history of patellar dislocations. The objective in Study II was to ascertain whether the location of a medial patellofemoral injury predicts the earliest onset of patellar redislocation. The setting of Study III was a randomized controlled trial where our ambition was to evaluate the benefits of a motion-restricting knee brace versus a neoprene nonhinged knee brace in the non-operative treatment of first-time patellar dislocation at 3-year follow-up. The aim of Study IV was to assess long-term cartilage deterioration in the knee joint after conservatively treated traumatic lateral patellar dislocation.

All four studies were conducted in the Department of Musculoskeletal Surgery at Tampere University Hospital. The diagnosis of patellar dislocation was verified with magnetic resonance imaging (MRI). Other notable ligamental injuries were also assessed from the MRI scans. The anatomic risk factors for recurrent patellar dislocation (tuberositas tibiae – trochlear groove distance, tuberositas tibiae – posterior cruciate ligament distance, sulcus angle, lateral inclination angle, and sulcus depth) were all measured. For the purposes of studies II and III, the medial patellofemoral ligament (MPFL) injury location was defined as patellar insertion, midsubstance area, femoral insertion, or a combination of these.

For Study I, 52 retrospectively assembled study patients were scanned bilaterally with MRI or computed tomography (CT) between 2005 and 2013 to assess rotational alignment. The control group consisted of 54 adult patients with no history of patellar dislocations. Both lower extremities of the patients were scanned with CT as part of a multitrauma protocol between March 2019 and September 2021 after being involved in a high energy trauma. The femoral anteversion of the patients in the study and control groups were then assessed from the rotational images.

The patients for Studies II and III were recruited between July 2012 and November 2015. Skeletally mature patients (aged at least 15 years, physes closed) with the suspicion of a first-time traumatic patellar dislocation were scanned with MRI during the first 3 weeks following the injury. The diagnosis of patellar dislocation was verified and other notable ligamental injuries assessed. Patients who underwent surgical treatment due to large osteochondral fragment and patients with anterior cruciate or posterior cruciate ligament injuries or recurring patellar dislocation during the first four weeks after injury were excluded from the analysis. A total of 64 patients formed the study population of Studies II and III.

The setting of Study III was a randomized controlled trial. Patients were randomized to two study groups: patella-stabilizing, motion-restricting knee brace (group A) and neoprene nonhinged knee brace (group B). During the 3-year follow- up, data were collected on patellar redislocations (primary outcome) or any instability symptoms in the PF joint, range of motion (ROM) of the knee, quadriceps muscle atrophy, Kujala and Tegner scores, Visual Analog Scale (VAS), rate of subsequent patella stabilizing surgery, and subjective symptoms of knee stiffness and weakness. Study IV consisted of 20 patients, who underwent follow-up MRI eight years after first-time traumatic patellar dislocation. Between 2005 and 2007, adult patients with a first-time patellar dislocation were primarily recruited to the study to evaluate bone bruise and cartilage injury to the patellofemoral (PF) joint. After eight years, patients were invited to attend a follow-up MRI to determine the progression of the cartilage lesions.

As a result of Study I, we found that patients with bilateral recurrent patellar dislocations have bilaterally greater femoral anteversion than patients without a history of patellar dislocation (23.2 vs. 12.4 degrees, CI, 5.6-16.0, p<0.001). Study II revealed that there was no medial patellofemoral injury location that could reliably predict the earliest onset of patellar redislocation. The mean time for patellar redislocation of patients with the MPFL injury at the femoral insertion was 25.0 months (range 5.5-23.5 months, SD 24.9), 42.6 months (range 17.2-60.7 months, SD 19.0) with the MPFL injury at the midsubstance area and 25.7 months (range 9.1- 43.4 months, SD 11.9) when the MPFL injury was at the patellar insertion (p=0.321). The primary outcome of Study III was that patients wearing a motion-restricting knee brace (Group A) did not have fewer patellar redislocations than patients wearing a neoprene nonhinged knee brace (Group B) in the treatment of a first-time patellar dislocation at 3 years of follow-up (11/32 patients (34.4%) vs. 12/32 patients (37.5%) (p=0.794, RD: -3.1%, 95% CI, -26.6 to 20.3). Patients who had knee ROM- restricting bracing (Group A) as a primary treatment for first-time traumatic patellar dislocation seemed to have patellar redislocations earlier than patients in Group B (21 vs. 38 months, p=0.053). Further, patients in the patellar stabilizing, motion restricting knee brace group had more quadriceps muscle atrophy during the first three months and their functional outcomes, according to Kujala score, were lower at six months after the injury.

In Study IV, cartilage injury of the PF joint in primary MRI was seen in 14/20 patients (70%). In the follow-up MRI, all the primary PF cartilage injuries were still evident. In addition, all those patients without cartilage injury in primary MRI had developed varying degrees of cartilage damage in the PF joint. Of 20 patients, 12 (60%) had ICRS III-IV cartilage lesions in at least one section of the PF joint in the follow-up MRI.
In conclusion, our results show that patients with bilateral recurrent patellar dislocations have bilaterally greater femoral anteversion than patients without a history of recurrent patellar dislocation. Further, the location of MPFL injury did not have statistically significant effect on the timing or rate of redislocations. However, an MPFL injury at the femoral insertion predicts decreased ROM of the knee and increased quadriceps muscle atrophy during the first three months after sustaining injury. The results of the randomized controlled trial revealed that the use of a patellar stabilizing, motion restricting knee brace for four weeks as nonoperative treatment after first-time traumatic patellar dislocation did not result in a reduction in the patellar redislocation rate. Immobilization of the knee was associated with more quadriceps muscle atrophy, slower regain of knee ROM, and lower functional outcome during the recovery, indicating the harmful effect on the sensitive extensor mechanism of the lower limb. Also, bone bruising and primary cartilage defects caused by traumatic patellar dislocation seem to have initiated the gradual degeneration of the cartilage in the patellofemoral joint during the eight years of follow-up. All these findings should encourage clinicians to consider proper meticulous rehabilitation and physiotherapeutic support in the management of traumatic patellar dislocation, as it is a serious injury involving various structures of the knee that might still affect physical performance many years after initial trauma.