- This systematic review of medical literature about acute hamstring injuries included 17 randomized controlled trials and 58 nonrandomized cohort studies, case–control studies and case series
- The reviewers concluded surgery offers substantial benefits over nonoperative care for the treatment of acute partial and complete proximal hamstring ruptures, whereas muscle injuries can be effectively treated with physical therapy
- The efficacy of platelet-rich plasma injections could not be determined because study protocols have varied widely
- The accuracy of predictions about recovery time can be improved with a thorough clinical examination, and structural factors observed on MRI scans can also guide estimates about return to play
Even though acute hamstring injury accounts for a significant absence from sports, little is known about optimal management of acute hamstring injury and factors associated with return to play (RTP).
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Scott D. Martin, MD, director of the Joint Preservation Service within the Department of Orthopaedics, Nathan H. Varady, MD, MBA, a sports medicine researcher in the department, and colleagues recently systematically reviewed the evidence. They provide guidance to fellow physicians in The Orthopaedic Journal of Sports Medicine.
In August 2020, the reviewers searched MEDLINE, the Cumulative Index to Nursing and Allied Health, the Cochrane Central Register of Controlled Trials and SPORTDiscus for relevant English-language randomized controlled trials, cohort studies, case–control studies and case series.
75 studies of sustained acute hamstring injury (<6 weeks between injury and initial examination) were included in the review. 17 were randomized controlled trials, 11 were comparative nonrandomized studies and 47 were noncomparative nonrandomized studies.
The reviewers were able to draw several conclusions about the management of acute hamstring injury:
- Patients who underwent surgery for proximal ruptures (partial or complete) have consistently better outcomes than those whose ruptures were managed nonoperatively
- For patients with acute muscle injuries, physical therapy using eccentric training and progressive agility and trunk stabilization is associated with a favorable RTP time, reinjury rate and restoration of strength; stretching-based protocols increase range of motion but do not increase strength and do not reduce reinjury risk
- Therapies that address neurological components of hamstring strain (e.g. slump stretching, reflexive release techniques) also have functional benefits
- Early initiation of rehabilitation with pain-threshold limits enables faster RTP and does not predispose to adverse effects
Studies of platelet-rich plasma injection weren't standardized enough to permit conclusions about efficacy.
Return to Play: Clinical Factors
17 studies investigated associations between clinical factors and time to RTP. Factors associated with accelerated RTP were:
- Less pain during outer-range strength testing
- Greater midrange strength as a percentage of uninjured leg strength
Factors associated with delayed RTP were:
- Greater passive knee extension of the uninjured leg
- Greater peak torque angle in knee extension
- Injury to the biceps femoris
- Greater pain at injury and initial evaluation
- Popping sound at injury
- Pain on resisted knee flexion
Some studies showed stretching-type injuries required longer recovery than sprinting-type injuries, while others found injury mechanisms did not affect recovery time.
Studies reported conflicting results about how RTP is affected by sex, level of play, injury grade, adherence to physical therapy, hip range of motion, history of other lower limb injury, and deficit in active knee extension.
Return to Play: MRI Factors
23 studies evaluated the role of MRI in predicting time to RTP. Accelerated RTP was linked to:
- MRI-negative injury
- A lower percentage of muscle/tendon involvement
- Shorter radiologist-predicted recovery
Factors associated with prolonged recovery time were:
- Greater lesion length
- A greater percentage of muscle/tendon involvement
- Complete tendinous/myotendinous rupture
- Complete central tendon disruption or "waviness"
- Greater number of muscles involved
Several studies showed the results of the initial clinical examination have much more bearing on RTP than MRI findings do.
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