Causal Relation Between Functional Muscular Dysbalance and Osteoarthritis

Author(s): Hajnovic L, Matziolis G, Schütz L, Röhner E

Purpose: An atrophy of quadriceps muscle is generally supposed to be a consequence of knee osteoarthritis. Anyway, there are recent studies pointing reversely at quadriceps sarcopenia as one of factors causing it. We assume that chronic functional muscular dysbalance is the key pathophysiologic momentum in genesis of primary knee osteoarthritis.

Materials and Methods: A prospective study carried out from August 2022 to October 2023. 39 Patients (20 male and 19 female), divided into four cohorts (A,B,C,D). Five Patients were examined bilaterally, hence we examined 44 extremities. We measured by ultrasound transversal planar surfaces of ventral and dorsal muscle groups of the thigh and set them into mutual relation. In the first group A, there were young patients of age about 20 years, without any previous history or complaints to the examined limb. We chose patients of age 30 years or more, with the same criteria for the second group B. There were patients with chronic lesions to dorsal medial meniscus, which is generally known as pre-arthrosis in group C. The group D contained patients with manifest knee osteoarthritis, planed for a TKA. The exclusion criteria of the last both groups were any previous surgery or trauma to the extremity, or eventual neurovascular impairment. Ethical approval was done by the Ethics Committee of the Sächsiche Landesärztekammer. All the procedures being performed were part of routine care (EK-BR-89/23-1).

Results: In the first group A, there was a ratio between transversal planar surfaces of ventral and dorsal muscle mass of about 1.86 (SD 0.46). One patient of the group had a history of prolonged immobility due to trauma. Excluding this patient, the ratio was about 2.0 (SD 0.27) and this could be considered as a physiological value in our opinion. We found substantial decline of ventral muscle mass during the lifetime, beginning already in the early 30s, with the ratio of about 1.39 (SD 0.3) within the group B. Unsurprisingly, the patient groups C and D, with manifest pre- or arthrosis, were affected the most, with ratios of about 1.16 (SD 0.28) and 1.1 (SD 0.25) respectively. We found also quadriceps atrophy on otherwise healthy contralateral lower extremities in both C and D groups, with average ratio 1.23 (SD 0.49), suggesting the ventral muscular atrophy could be setting on first, causing further osteoarthritic changes of the joint, in these cases yet to come. The dorsal thigh muscle mass showed during the lifetime rather constant volumes, with average for group A about 189,3cm² (SD 44.9) and group B even 202cm² (SD 46.3). The quadriceps surface in group C was about 212.4cm² (SD 81.2) and 189.8cm² (SD 76.7) for posterior muscles, the average surface of group D was 193.8cm² (SD 102) for quadriceps and 183.6cm² (SD 100) for dorsal muscles. There seems to be some significance of the gastrocnemius muscle in relation to knee osteoarthritis also, as we noticed volume decline throughout lifetime, with 98cm² (SD 27.8) for A, and 75cm² (SD 27.8) for group B.

Conclusion: The primary knee osteoarthritis could be a consequence of long-term dysbalance of adjacent muscle groups, developing slowly during the lifetime, with progressive quadriceps atrophy. The functionally dominant dorsal thigh muscles retain stable volumina during the whole life span and throughout all patient groups, regardless of the onset of osteoarthritis, with average surfaces of 191.2cm² (SD 7.7). In contrary, the antagonistic ventral muscle gradually decreases in mass during the time, from average 340cm2 in the group A to just 224cm² (SD 96.2) within the subgroup B of age over 50 years. Physical inactivity or muscular atrophy due to knee pathology cannot explain this phenomenon, as we found it even in athletic individuals and the sarcopenia affects only one muscle group of both. We assume the spinal inhibitory reflex has a decisive role in pathophysiology of osteoarthritis generally. Functionally dominant, e.g. postural muscle groups, via spinal reflex inhibit their antagonists, with imbalanced joint strength equilibrium as a consequence. Moreover, in this case consecutive physical shortening of hamstrings shift femoral condyle due to tibial slope dorsally, leading to wrong joint kinematics, focal pressure peaks and amplified rollback with mechanical conflict between medial femoral condyle and dorsal part of medial meniscus. The anterior cruciate ligament elongation can be also viewed as a result of prolonged sagittal knee dysbalance. We believe systematic training ("up-tuning" via drill) of functionally recessive quadriceps muscle could pose a strategy to prevent farther development of osteoarthritis. Furthermore, proper muscular balance could be one of the key issues in longterm arthroplasty survival.