ABSTRACT

There is a paucity of literature on patient-reported outcome measures (PROMs) following proximal hamstring repair beyond return to play, patient satisfaction and pain improvement. The minimal clinically important difference (MCID) defines the minimum degree of quantifiable improvement that a patient can perceive, but the MCID and predictors of this measure have not been defined for this patient population. This study aimed to define the MCID and determine the efficacy of open proximal hamstring repair through achievement of MCID and identify characteristics predictive of achieving MCID. A retrospective cohort review of an institutional hip registry was conducted, analyzing the modified Harris Hip Score (mHHS) and International Hip Outcome Tool (iHOT-33). MCID was calculated using a distribution-based method. Demographic and clinical variables predictive of achieving MCID were analyzed using univariable and multivariate logistic regression analyses. Thirty-nine patients who underwent open proximal hamstring repair were included. The mean patient age was 48.5 ± 12.4 years, with a mean follow-up of 37.1 ± 28 months. The MCID was determined for each PROM (mHHS—11.8; iHOT-33—12.6). A high percentage of patients achieved MCID for both PROMs (mHHS—85.7%; iHOT-33—91.4%). Univariate logistical regression demonstrated increased age (P = 0.163), increased body mass index (BMI; P = 0.072), requirement for inpatient admission (P = 0.088) and pre-operative iHOT-33 (P = 0.104) trended towards clinically significant predictors of not achieving MCID. A high percentage of patients achieved MCID while age, BMI, inpatient admission and pre-operative iHOT-33 appear to influence the achievement of clinically significant outcome in patients undergoing open proximal hamstring repair.

INTRODUCTION

Hamstring strains account for 25–30% of all muscle strains, making this injury the most common muscle strain in the body [1–6]. A majority of these injuries occur at the myotendinous junction and can be treated non-operatively; however, up to 12% involve a tear or avulsion at the proximal hamstring origin [7–9]. Non-operative treatment of retracted and/or complete tears can result in intractable pain, atrophy, weakness and scarring to the sciatic nerve resulting in radicular pain patterns [10, 11]. As a result, surgical intervention is often recommended, especially for young and athletic populations. Furthermore, the frequency of proximal hamstring injuries appears to be on the rise as the middle-aged population has become more physically active and now represents a larger percentage of the patients presenting with a proximal hamstring injury [3].

Patient-reported outcome measures (PROMs) are now established as standard for defining treatment success. As previously defined in the literature, minimal clinically important difference (MCID) is the smallest change in the outcome that a patient is able to appreciate clinically [12–15]. When deciding which is the best treatment for a patient undergoing a surgical proximal hamstring repair, little research has been conducted on patient outcomes beyond patient satisfaction, return to play and pain improvement [16–18]. More specifically, psychometric measures such as MCID of patient-reported hip outcomes have not been determined in this patient population.

Assessing the achievement of meaningful outcome for the operative treatment of proximal hamstring tendon injury is important in order to allow for a more accurate assessment of the efficacy of treatment interventions. The purpose of this study is to (i) define the MCID of patient-reported hip outcomes and determine the efficacy of open proximal hamstring repair and (ii) identify patient and injury characteristics predictive of achieving MCID post-operatively.

METHODS Patient enrollment and data collection

After institutional review board approval, a retrospective review was performed on a consecutive series of patients who underwent open proximal hamstring repair between September 2010 and April 2019. Patient and operative demographics, clinical data, and patient-reported outcomes were prospectively collected in a secure institutional registry. Indications for proximal hamstring repair were as follows: partial avulsions that have failed non-operative management for a minimum of 6 months, 2-tendon tears with >2 cm of retraction in young active patients and 3-tendon tears [19]. Exclusion criteria included: incomplete pre-operative or 1-year post-operative PROMs, concomitant procedures beyond hamstring repair and prior operative treatment of the ipsilateral proximal hamstring. Acuity of the injury was defined as follows: acute (≤6 weeks) and chronic (>6 weeks).

Operative technique

All open proximal hamstring repairs were performed by one of three fellowship-trained sports medicine surgeons at a high-volume tertiary care hospital. Patients are placed in the prone position with the operative leg free allowing knee flexion to relieve hamstring tension during repair. A microvascular trained co-surgeon (hand or plastic surgeon) is frequently used to assist with exposure, especially for chronic cases where significant scar tissue is expected and for cases where a neurolysis was indicated. The decision to use a transverse gluteal incision versus a longitudinal incision is largely dictated by the co-surgeons preference. The gluteal fascia is opened and the gluteus maximus is retracted proximally. The hamstring fascia is then opened and the retracted tendon is identified. Prior to the placement of deep retractors around the ischium, the sciatic nerve is identified and protected, and a neurolysis is performed when indicated. Care is taken to protect the posterior femoral cutaneous nerve, which can be traced proximally to aid in identification of the sciatic nerve. The ruptured proximal hamstring tendon is identified and mobilized. Deep Hohmann retractors are placed to expose the ischial tuberosity, which is then debrided of soft tissue to create a bleeding bony surface to facilitate biological healing. The number of anchors placed in the ischial tuberosity for repair depends on the size of the tear and quality of the tendon. Once the anchors are placed, the free sutures from the anchors are passed through the tendon edges. The knee is flexed to relieve tension on the hamstring tendon while the sutures are tied. Adequate re-approximation of the tendon to the ischial tuberosity is confirmed. The wound is copiously irrigated and closed in layers. Patients are placed in a hinged knee brace to maintain knee flexion in order to prevent tension on the repair.

Post-operative rehabilitation protocol

The post-operative rehabilitation regime was standardized for all proximal hamstring repairs. A full-time knee brace is used for 6 weeks to keep the knee flexed to 30°, limiting tension on the repair site and weight bearing is limited to toe touch weight bearing. During the next 6 weeks, patients are progressed to full weight bearing, weaned from their brace and assistive devices as tolerated. At 12 weeks post-operatively, patients are permitted to begin strengthening exercises. Patients are allowed to return to activities as tolerated no sooner than 16 weeks post-operatively. Return to sport criteria is defined based on (i) dynamic neuromuscular control with multi-plane activities at high velocity without pain or swelling; (ii) less than 10% deficit for side-to-side hamstring comparison on Biodex testing and (iii) less than 10% deficit on functional testing profile.

Patient-reported clinical outcomes

The modified Harris Hip Score (mHHS) and International Hip Outcome Tool (iHOT-33) were obtained pre-operatively and at final follow-up. To identify differences in meaningful outcome improvement in patients undergoing open proximal hamstring repair, the MCID was calculated using the distribution-based method. This method involved calculating the half standard deviation for the mHHS and iHOT-33 in the current study, consistent with previous studies [12–15, 20].

Statistical analysis

Patient demographics assessed included length of follow-up, laterality, sex, age, BMI, smoking history and history of diabetes. Injury demographics assessed included mechanism, number of tendons involved, tendon retraction, presence of neurological symptoms, acuity, number of anchors used for repair, presence of a plastic surgeon for exposure, disposition and length of stay. The mean and standard deviation were reported for continuous variables. Continuous data were analyzed with paired t-tests. Univariate logistical regression analysis was performed to assess associations between achieving MCID and demographic variables. Multivariate conditional logistic regression analysis was performed on variables demonstrating a P-value < 0.15 during univariate logistic regression analysis. Statistical analyses were conducted using SPSS statistical software (IBM SPSS Statistics for Windows, version 25.0.0; Armonk, NY: IBM Corp).

RESULTS

One hundred and sixteen patients were identified in the Hospital for Special Surgery Hip Registry, with 39 patients included in this study after the application of the inclusion/exclusion criteria (Fig. 1). The mean follow-up was 37.1 ± 28.0 months. A majority of the patients were female (66.7%), with a relatively even distribution in laterality. The mean patient age was 48.5 ± 12.4 years. No patients were diabetic, while 12.8% of patients reported a smoking history (Table I).

. N . Percentage . Mean . SD . Range . Age (years)   48.5 12.4 19–68 BMI (kg/m2)   25.3 3.9 18.9–33.9 Follow-up (months)   37.1 28.0 10–112 Total 39 100.0    Laterality Right 21 53.8    Left 18 46.2    Sex Female 26 66.7    Male 13 33.3    Smoking status Yes 5 12.8    No 31 79.5    Unknown 3 7.7    Diabetic Yes  0.0    No 37 94.9    Unknown 2 5.1     . N . Percentage . Mean . SD . Range . Age (years)   48.5 12.4 19–68 BMI (kg/m2)   25.3 3.9 18.9–33.9 Follow-up (months)   37.1 28.0 10–112 Total 39 100.0    Laterality Right 21 53.8    Left 18 46.2    Sex Female 26 66.7    Male 13 33.3    Smoking status Yes 5 12.8    No 31 79.5    Unknown 3 7.7    Diabetic Yes  0.0    No 37 94.9    Unknown 2 5.1     . N . Percentage . Mean . SD . Range . Age (years)   48.5 12.4 19–68 BMI (kg/m2)   25.3 3.9 18.9–33.9 Follow-up (months)   37.1 28.0 10–112 Total 39 100.0    Laterality Right 21 53.8    Left 18 46.2    Sex Female 26 66.7    Male 13 33.3    Smoking status Yes 5 12.8    No 31 79.5    Unknown 3 7.7    Diabetic Yes  0.0    No 37 94.9    Unknown 2 5.1     . N . Percentage . Mean . SD . Range . Age (years)   48.5 12.4 19–68 BMI (kg/m2)   25.3 3.9 18.9–33.9 Follow-up (months)   37.1 28.0 10–112 Total 39 100.0    Laterality Right 21 53.8    Left 18 46.2    Sex Female 26 66.7    Male 13 33.3    Smoking status Yes 5 12.8    No 31 79.5    Unknown 3 7.7    Diabetic Yes  0.0    No 37 94.9    Unknown 2 5.1    

Fig. 1.

CONSORT diagram of patient inclusion into the current retrospective study.

Fig. 1.

CONSORT diagram of patient inclusion into the current retrospective study.

Running was the mechanism of injury in 15.4% of the cases, with 28.2% of all injuries resulting from a traumatic mechanism. Tendon retraction was noted in 46.2% of cases, and 10 patients (25.6%) had 5 cm or more of tendon retraction at the time of presentation. A previous study indicated increased difficult to perform the proximal hamstring repair when tendon retraction was >5 cm [21]. Only two patients (5.1%) presented with neurological symptoms. A majority of the repairs were performed using a two (43.6%) or three (28.2%) anchor repair. Patients were frequently admitted overnight and discharged on Post-operative Day 1 (Table II).

. N . Percentage . Mechanism (Running) Yes 6 15.4 No 27 69.2 Unknown 6 15.4 Mechanism (Traumatic) Yes 11 28.2 No 22 56.4 Unknown 6 15.4 Tendons involved 1–2 10 25.6 3 10 25.6 Unknown 19 48.7 Retraction Yes 18 46.2 No 6 15.4 Unknown 15 38.5 Retraction distance <5 cm 14 35.9 ≥5 cm 10 25.6 Unknown 15 38.5 Neurological symptoms Yes 2 5.1 No 35 89.7 Unknown 2 5.1 Acuity Acute 15 38.5 Chronic 22 56.4 Unknown 2 5.1 Number of anchors 1 5 12.8 2 17 43.6 3 11 28.2 Unknown 2 5.1 Microvascular surgeon assistance Yes 31 79.5 No 6 15.4 Unknown 2 5.1 Disposition Inpatient 35 89.7 Outpatient 2 5.1 Unknown 2 5.1 Length of stay 0–1 30 76.9 2–6 7 17.9 Unknown 2 5.1  . N . Percentage . Mechanism (Running) Yes 6 15.4 No 27 69.2 Unknown 6 15.4 Mechanism (Traumatic) Yes 11 28.2 No 22 56.4 Unknown 6 15.4 Tendons involved 1–2 10 25.6 3 10 25.6 Unknown 19 48.7 Retraction Yes 18 46.2 No 6 15.4 Unknown 15 38.5 Retraction distance <5 cm 14 35.9 ≥5 cm 10 25.6 Unknown 15 38.5 Neurological symptoms Yes 2 5.1 No 35 89.7 Unknown 2 5.1 Acuity Acute 15 38.5 Chronic 22 56.4 Unknown 2 5.1 Number of anchors 1 5 12.8 2 17 43.6 3 11 28.2 Unknown 2 5.1 Microvascular surgeon assistance Yes 31 79.5 No 6 15.4 Unknown 2 5.1 Disposition Inpatient 35 89.7 Outpatient 2 5.1 Unknown 2 5.1 Length of stay 0–1 30 76.9 2–6 7 17.9 Unknown 2 5.1  . N . Percentage . Mechanism (Running) Yes 6 15.4 No 27 69.2 Unknown 6 15.4 Mechanism (Traumatic) Yes 11 28.2 No 22 56.4 Unknown 6 15.4 Tendons involved 1–2 10 25.6 3 10 25.6 Unknown 19 48.7 Retraction Yes 18 46.2 No 6 15.4 Unknown 15 38.5 Retraction distance <5 cm 14 35.9 ≥5 cm 10 25.6 Unknown 15 38.5 Neurological symptoms Yes 2 5.1 No 35 89.7 Unknown 2 5.1 Acuity Acute 15 38.5 Chronic 22 56.4 Unknown 2 5.1 Number of anchors 1 5 12.8 2 17 43.6 3 11 28.2 Unknown 2 5.1 Microvascular surgeon assistance Yes 31 79.5 No 6 15.4 Unknown 2 5.1 Disposition Inpatient 35 89.7 Outpatient 2 5.1 Unknown 2 5.1 Length of stay 0–1 30 76.9 2–6 7 17.9 Unknown 2 5.1  . N . Percentage . Mechanism (Running) Yes 6 15.4 No 27 69.2 Unknown 6 15.4 Mechanism (Traumatic) Yes 11 28.2 No 22 56.4 Unknown 6 15.4 Tendons involved 1–2 10 25.6 3 10 25.6 Unknown 19 48.7 Retraction Yes 18 46.2 No 6 15.4 Unknown 15 38.5 Retraction distance <5 cm 14 35.9 ≥5 cm 10 25.6 Unknown 15 38.5 Neurological symptoms Yes 2 5.1 No 35 89.7 Unknown 2 5.1 Acuity Acute 15 38.5 Chronic 22 56.4 Unknown 2 5.1 Number of anchors 1 5 12.8 2 17 43.6 3 11 28.2 Unknown 2 5.1 Microvascular surgeon assistance Yes 31 79.5 No 6 15.4 Unknown 2 5.1 Disposition Inpatient 35 89.7 Outpatient 2 5.1 Unknown 2 5.1 Length of stay 0–1 30 76.9 2–6 7 17.9 Unknown 2 5.1  Minimal clinically important difference analysis

Patients in the cohort experienced a statistically significant mean improvement in their pre- (53.7 ± 19.8) to post-operative (90.1 ± 14.7) mHHS (P-value < 0.01). The distribution-based MCID for the mHHS was 11.8. Post-operatively, 30 patients (85.7%) achieved MCID (Table III). Similarly, patients experienced a statistically significant mean improvement in their pre- (37.9 ± 16.2) to post-operative (84.4 ± 20.5) iHOT-33 (P-value < 0.01). The distribution-based MCID for the iHOT-33 was 12.6. Post-operatively, 32 patients (91.4%) achieved MCID (Table III).

. N . Percentage . Mean . SD . Range . mHHS Pre-operative   53.7 19.8 7.7–95.7 Post-operative   90.1 14.7 42.9–100 Net change   37.0 23.5 −14.3–84.6 P-value <0.01     Distribution-based MCID 11.8     Patients achieving MCID      Yes 30 85.7    No 5 14.3    iHOT-33 Pre-operative   37.9 16.2 15.2–72.7 Post-operative   84.8 20.5 17.5–100 Net change   46.6 25.2 −37.1–83.4 P-value <0.01     Distribution-based MCID 12.6     Patients achieving MCID      Yes 32 91.4    No 3 8.6     . N . Percentage . Mean . SD . Range . mHHS Pre-operative   53.7 19.8 7.7–95.7 Post-operative   90.1 14.7 42.9–100 Net change   37.0 23.5 −14.3–84.6 P-value <0.01     Distribution-based MCID 11.8     Patients achieving MCID      Yes 30 85.7    No 5 14.3    iHOT-33 Pre-operative   37.9 16.2 15.2–72.7 Post-operative   84.8 20.5 17.5–100 Net change   46.6 25.2 −37.1–83.4 P-value <0.01     Distribution-based MCID 12.6     Patients achieving MCID      Yes 32 91.4    No 3 8.6     . N . Percentage . Mean . SD . Range . mHHS Pre-operative   53.7 19.8 7.7–95.7 Post-operative   90.1 14.7 42.9–100 Net change   37.0 23.5 −14.3–84.6 P-value <0.01     Distribution-based MCID 11.8     Patients achieving MCID      Yes 30 85.7    No 5 14.3    iHOT-33 Pre-operative   37.9 16.2 15.2–72.7 Post-operative   84.8 20.5 17.5–100 Net change   46.6 25.2 −37.1–83.4 P-value <0.01     Distribution-based MCID 12.6     Patients achieving MCID      Yes 32 91.4    No 3 8.6     . N . Percentage . Mean . SD . Range . mHHS Pre-operative   53.7 19.8 7.7–95.7 Post-operative   90.1 14.7 42.9–100 Net change   37.0 23.5 −14.3–84.6 P-value <0.01     Distribution-based MCID 11.8     Patients achieving MCID      Yes 30 85.7    No 5 14.3    iHOT-33 Pre-operative   37.9 16.2 15.2–72.7 Post-operative   84.8 20.5 17.5–100 Net change   46.6 25.2 −37.1–83.4 P-value <0.01     Distribution-based MCID 12.6     Patients achieving MCID      Yes 32 91.4    No 3 8.6     Logistic regression analysis

On univariate logistic regression analysis, no variables were found to have a statistically significant association with achieving the MCID on the mHHS; however, age (P-value = 0.163) and BMI (P-value = 0.072) were near-significant predictors for not achieving MCID. Multivariate logistic regression analysis of these variables did not reach statistical significance for an association between age (P-value = 0.564) and BMI (P-value = 0.518) and achieving post-operative mHHS MCID (Table IV).

Table IV.

Logistic regression analysis for variables associated with achieving MCID for mHHS

. Univariate analysis (P-value) . Multivariate analysis (P-value) . Attending surgeon 0.380  Laterality 1.000  Sex 0.337  Age 0.163* 0.564 BMI 0.072* 0.518 Smoking 1.000  Mechanism (Running) 1.000  Mechanism (Traumatic) 1.000  Tendons involved 1.000  Retraction 0.537  Retraction distance 1.000  Neurological symptoms 1.000  Acuity 0.625  Implant 0.454  Number of anchors 0.572  Microvascular surgeon assistance 1.000  Disposition 0.284  Length of stay 1.000  Follow-up 0.394  Pre-operative mHHS 0.394   . Univariate analysis (P-value) . Multivariate analysis (P-value) . Attending surgeon 0.380  Laterality 1.000  Sex 0.337  Age 0.163* 0.564 BMI 0.072* 0.518 Smoking 1.000  Mechanism (Running) 1.000  Mechanism (Traumatic) 1.000  Tendons involved 1.000  Retraction 0.537  Retraction distance 1.000  Neurological symptoms 1.000  Acuity 0.625  Implant 0.454  Number of anchors 0.572  Microvascular surgeon assistance 1.000  Disposition 0.284  Length of stay 1.000  Follow-up 0.394  Pre-operative mHHS 0.394  Table IV.

Logistic regression analysis for variables associated with achieving MCID for mHHS

. Univariate analysis (P-value) . Multivariate analysis (P-value) . Attending surgeon 0.380  Laterality 1.000  Sex 0.337  Age 0.163* 0.564 BMI 0.072* 0.518 Smoking 1.000  Mechanism (Running) 1.000  Mechanism (Traumatic) 1.000  Tendons involved 1.000  Retraction 0.537  Retraction distance 1.000  Neurological symptoms 1.000  Acuity 0.625  Implant 0.454  Number of anchors 0.572  Microvascular surgeon assistance 1.000  Disposition 0.284  Length of stay 1.000  Follow-up 0.394  Pre-operative mHHS 0.394   . Univariate analysis (P-value) . Multivariate analysis (P-value) . Attending surgeon 0.380  Laterality 1.000  Sex 0.337  Age 0.163* 0.564 BMI 0.072* 0.518 Smoking 1.000  Mechanism (Running) 1.000  Mechanism (Traumatic) 1.000  Tendons involved 1.000  Retraction 0.537  Retraction distance 1.000  Neurological symptoms 1.000  Acuity 0.625  Implant 0.454  Number of anchors 0.572  Microvascular surgeon assistance 1.000  Disposition 0.284  Length of stay 1.000  Follow-up 0.394  Pre-operative mHHS 0.394  

On univariate logistic regression analysis, no variables were found to have a statistically significant association with achieving the MCID on the iHOT-33; however, requirement for inpatient admission (P-value = 0.088) and pre-operative iHOT-33 (P-value = 0.104) were near-significant predictors for not achieving MCID on the iHOT-33. Multivariate logistic regression analysis of these variables did not reach statistical significance for an association between requirement for inpatient admission (P-value = 1.00) and pre-operative iHOT-33 (P-value = 0.437) and achieving post-operative iHOT-33 MCID (Table V).

Table V.

Logistic regression analysis for variables associated with achieving MCID for iHOT-33

. Univariate analysis (P-value) . Multivariate analysis (P-value) . Attending surgeon 0.712  Laterality 0.234  Sex 1.000  Age 0.241  BMI 0.747  Smoking 1.000  Mechanism (Running) 0.446  Mechanism (Traumatic) 0.532  Tendons involved 0.474  Retraction 0.486  Retraction distance 0.429  Neurological symptoms 1.000  Acuity 1.000  Implant 1.000  Number of anchors 0.392  Microvascular surgeon assistance 0.453  Disposition 0.088* 1.000 Length of stay 1.000  Follow-up 0.729  Pre-operative mHHS 0.104* 0.437  . Univariate analysis (P-value) . Multivariate analysis (P-value) . Attending surgeon 0.712  Laterality 0.234  Sex 1.000  Age 0.241  BMI 0.747  Smoking 1.000  Mechanism (Running) 0.446  Mechanism (Traumatic) 0.532  Tendons involved 0.474  Retraction 0.486  Retraction distance 0.429  Neurological symptoms 1.000  Acuity 1.000  Implant 1.000  Number of anchors 0.392  Microvascular surgeon assistance 0.453  Disposition 0.088* 1.000 Length of stay 1.000  Follow-up 0.729  Pre-operative mHHS 0.104* 0.437 Table V.

Logistic regression analysis for variables associated with achieving MCID for iHOT-33

. Univariate analysis (P-value) . Multivariate analysis (P-value) . Attending surgeon 0.712  Laterality 0.234  Sex 1.000  Age 0.241  BMI 0.747  Smoking 1.000  Mechanism (Running) 0.446  Mechanism (Traumatic) 0.532  Tendons involved 0.474  Retraction 0.486  Retraction distance 0.429  Neurological symptoms 1.000  Acuity 1.000  Implant 1.000  Number of anchors 0.392  Microvascular surgeon assistance 0.453  Disposition 0.088* 1.000 Length of stay 1.000  Follow-up 0.729  Pre-operative mHHS 0.104* 0.437  . Univariate analysis (P-value) . Multivariate analysis (P-value) . Attending surgeon 0.712  Laterality 0.234  Sex 1.000  Age 0.241  BMI 0.747  Smoking 1.000  Mechanism (Running) 0.446  Mechanism (Traumatic) 0.532  Tendons involved 0.474  Retraction 0.486  Retraction distance 0.429  Neurological symptoms 1.000  Acuity 1.000  Implant 1.000  Number of anchors 0.392  Microvascular surgeon assistance 0.453  Disposition 0.088* 1.000 Length of stay 1.000  Follow-up 0.729  Pre-operative mHHS 0.104* 0.437  Complications

Six patients (15.4%) experienced a total of seven post-operative complications (Table VI). Deep infection (two patients, 5.1%) and superficial vein thrombophlebitis (two patients, 5.1%) were the most common complications. One patient (2.6%) experienced a pudendal nerve injury post-operatively.

. N .