Do patients with anterior cruciate ligament (ACL) tears demonstrate muscle strength deficits of the hip, knee, and ankle muscles?

Anterior cruciate ligament injuries are common with a median annual incidence of 0.03% per person overall and up to 3.7% in professional athletes (1). Approximately 50% of individuals with an ACL tear can manage non-surgically (2, 3), with surgical reconstruction indicated for those reporting persistent knee instability (4, 5). The hamstrings, soleus, and gluteus medius muscles assist the ACL by resisting anterior tibial translation and knee valgus moments (6). Despite this, clinical practice guidelines recommend the assessment of quadriceps and hamstrings strength alone to guide rehabilitation. Increased hamstrings and reduced soleus activity has been demonstrated in male athletes following ACL reconstruction (7) but there is a lack of information in patients being managed non-operatively.

Identifying muscle strength impairments of the hip, knee and ankle, and developing clinical strategies that address such impairments with physiotherapy rehabilitation may reduce the need for patients to undergo surgical intervention as well as decrease the associated costs and risks of progression to chronic diseases. Addressing muscle strength deficits before surgery (prehabilitation) may also benefit patients post-operatively, which is advocated in clinical practice guidelines for the quadriceps and hamstrings muscles (8, 9), but not the soleus or gluteus medius muscles specifically.

The PhD studentship will be a clinical study of prospective, repeated measures design performed at Aintree University Hospital, Therapies Department, Liverpool University Hospitals NHS Foundation Trust. Projects will be conducted in collaboration with relevant international experts; therefore students will have the opportunity to collaborate with, learn from, and be supported by leaders in the field both domestically and internationally. The aim of the study will be to determine if patients with ACL tears have hamstring, soleus, and gluteus medius muscle strength deficit.

Hamstrings, soleus, and gluteus medius muscle strength will be measured in MRI-confirmed ACL injured patients before commencing rehabilitation. Quadriceps and hamstrings strength will be quantified using isokinetic electromechanical dynamometry (HUMAC NORM Cybex). Soleus and gluteus medius muscle strength will be quantified with an isometric seated calf raise and isometric hip abduction respectively (Force Frame, Vald). Participants will be considered to have no strength impairment if limb symmetry is <10% (comparison with the uninjured side) and absolute values are above normative reference values for the specific muscle groups. For those with strength impairments, targeted rehabilitation will be performed until the impairments have been addressed, as indicated by repeated measurement.

Statistical analyses will be performed to determine whether strength deficits exist between the injured and uninjured sides. Primary outcome measures will be force and torque values recording with dynamometry. Secondary outcome measures will be single leg jump height and single leg drop jump metrics (contact time and reactive strength index) measured on force plates (Force decks, Vald), the IKDC and ACL-RSI questionnaires, and number of patients proceeding to ACL reconstruction surgery.