The influence of strength capacity on outcome after knee joint dislocation: a four-year follow-up.

The aim of this project was to assess the strength values four years after MLKI and compare them to patient reported outcomes, jump performance and osteoarthritis progression.

For this retrospective case series, 22 subjects (5 females, 17 males, mean age 45 ±15 years) 49 ±16 months after surgical treatment of a MLKI were recruited and included in the study. The follow-up consisted of isokinetic strength testing evaluating peak torque (Nm/kg) as well as single and triple hop testing. In addition, 1.5T magnetic resonance imaging (MRI) to document osteoarthritis progression classified from grade 0 to 4 by Park et al. (2013) was performed and the participants filled in four questionnaires, the Tegner Activity Scale (TAS), the International Knee Documentation Committee (IKDC), the Lysholm Score, and the Anterior Cruciate Ligament – Return to Sport Injury Scale (ACL-RSI).

The knee extensor force reached a limb symmetry index (LSI) of 75.5 ±19.5% and a relative force of 1.5 ±0.54 Nm/kg. Jumping performance of both the healthy and affected side correlated highly significant with knee extensor force (r=0.871, p0.001, R²=0.759, resp. r=0.864, p0.001, R²=0.731) and showed good symmetry with a LSI of 92.8%. Relative quadriceps force showed significant difference of 0.898 Nm/kg with strong effect size regarding osteoarthritis progression between grade 0 and 4 in the medial compartment (p=0.024, Cohen’s d=1.328) and high significant difference with strong effect size in the patellofemoral compartment (p0.001, ω2=0.507). In addition, there was a mean correlation of r=0.43 (p=0.046, R²=0.19) between strength and IKDC. The questionnaires showed good mean scores of 5.18 (TAS), 72.62 (IKDC), 84.36 (Lysholm Score), and 65.41 (ACL-RSI).

Quadriceps strength was significantly reduced at four years postoperatively, both in comparison to the opposite side and in relation to body weight. Functional scores (Hop Test) seem to overestimate the knee function. These deficits might explain, among other things, the subjective questionnaire scores and reduced knee function.

Participants reached an acceptable symptom state but were still significantly weak in comparison to healthy populations from other studies. The strength of the knee extensor is linked to the ability to walk and sprint, knee function, secondary injuries of the knee and the long-term development of knee osteoarthritis. Restoring quadriceps strength and control has therefore to be one of the main goals in the rehabilitation of MLKI. A continuous strength training might be protective for knee joint health after suffering a MLKI.