Patient-reported outcomes after surgical and non-surgical treatment of proximal hamstring avulsions in middle-aged patients

Study design and setting

A single-centre retrospective cohort study on patients treated from 2007 to 2013 at an academic university tertriary care centre. It is one of the five major emergency hospitals in the Stockholm area, with a catchment area of approximately 500 000 inhabitants. The guidelines of the STRrengthening the Reporting of OBservational studies in Epidemiology statement were followed.

Participants

We included patients with a proximal avulsion injury during the study period and identified them from the following: (A) all MRI exams at our department where the radiologist described a proximal hamstring injury and (B) from the digital surgical administrative system, in which surgical codes indicated surgery for proximal hamstring injury. We excluded patients with Wood type 1 and 24 (no avulsed tendons or bony avulsion on MRI), those with inconclusive MRIs and those with a previous hamstring injury or previous surgery of the thigh or knee in the affected leg (table 1). All participants gave their informed consent. A flow chart of patient enrolment is demonstrated in figure 1.

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Variables

Exposure

The choice of treatment was decided at the outpatient clinic after the MRI diagnosis. Our treatment algorithm is a combined assessment of age (with younger patients more likely to receive surgical treatment), where ASA 3 or 4 indicates high comorbidity and is more likely to receive non-surgical treatment, the patient’s subjective activity level (high performance amateur athletes were more likely to receive surgical treatment), MRI findings (patients with Wood type 5 with more than 2 cm retraction were offered surgical treatment) and clinical findings. Lastly, the most commonly used clinical test in our department is the hip extension test, in which the patient is asked to extend the hip in prone position. Surgery is favoured when the patient is unable to extend the hip (figure 2).

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Figure 2

Hip extension test. When patient can lift the affected leg from prone position as shown in the picture, non-surgical treatment is the favoured option. Photo by: S Jonhagen

Interventions

Data collection and follow-up

The baseline data and demographics (age, sex, ASA classification, type of activity at injury, registered clinical findings and MRI findings) were collected from the hospital administrative data collection systems for surgery and radiology collected in the same manner for both groups. We also registered the time from injury to the start of treatment, surgeon, surgical incision and registered complications.

At follow-up, all included participants were sent two patient-reported outcome measurement questionnaires: the LEFS and PHIQ. The questionnaires were resent twice to those who did not respond. Those who declined to reply per post were phoned by the first author (E Pihl).

Statistical methods

Descriptive statistics (means and SD) were used to describe the patient characteristics and outcome variables. Fischer’s exact test was used for categorical variables and Student’s t-test for continuous variables. A linear regression analysis was performed to adjust for confounders that could affect the primary outcome. The statistical model included the exposure variable and confounders (ie, surgery/non-surgery group, age, sex, ASA classification and tendon retraction ≥2 cm). All analyses were considered statistically significant at a p value of ≤0.05. The statistical analyses were performed using SPSS V.23 for Mac. A power analysis was not preformed prior to the study.

Participants and descriptive data

We enrolled 47 patients (29 males, mean (SD) age 51 (9) years, all except one within the age range of 34–68 years), 33 in the surgery group and 14 in the non-surgery group completed the follow-up at a mean (SD) of 3.9 (1.4) years (range: 2.0–7.3 years) (figure 2). The only outlier was 23 years and was surgically treated. The baseline characteristics of the two groups were similar except for the MRI, in which the surgical treated group had a larger proportion of tendons with a retraction ≥2 cm (p=0.025) (table 2). Four orthopaedic consultants performed the surgeries. In the surgically treated group, one patient suffered a postoperative pulmonary thrombosis, one patient suffered a wound infection and one patient suffered from severe persistent pain postoperatively. There were no adverse events in the non-surgically treated group. In one patient, nerolysis of the sciatic nerve was preformed.

Main results

We found no association between the treatment arm and our primary outcomes. The LEFS score was 72 (SD ±16) in the non-surgically treated group and 74 (SD ±12) in the surgically treated group (p=0.80) (table 3). When adjusting for confounders in the linear regression model, only increasing age was associated with a lower LEFS score (B −0.5 (95% CI −0.9 to −0.0), p=0.037). Most patients in both groups received their treatment in the acute phase within 4 weeks after the injury.

In addition, we found no significant difference between the groups regarding pain or stiffness and numbness in the injured leg. The proportion of patients who regularly used analgetics for their proximal hamstring injury at the time of follow-up was similar in both groups, 21% in the non-surgically treated group and 18% in the surgically treated group. Twenty-one per cent of non-surgically treated and 31% of surgically treated patients who experienced numbness in the injured leg (table 3). Eighty-nine per cent of the patients regarded themselves as high-performance amateur athletes at the time of follow-up, and although this proportion was slightly higher in the surgically treated group (94% vs 79%), this did not reach statistical significance. The only statistically significant difference in our outcome variables was the total hours per week the patients were performing physical activity at the time of follow-up, p=0.02 (table 3).

Strengths

The two key strengths of this study are that the follow-up is performed using a validated questionnaire, the LEFS, and only 5 of 52 subjects who were assessed as eligible were lost to follow-up. Previous publications found a significant correlation between return to activity, hamstring muscle strength and the single-leg hop test.7 This indicates that LEFS is a validated patient-reported outcome measure and an indicator of the objective function for patients treated for proximal hamstring avulsions. It is notable that the LEFS scores in our study match the LEFS scores in previous studies both for surgically7 10 11 and non-surgically1 2 treated cohorts. In addition to this, we also assessed treatment outcomes quantitatively with patient-reported length of physical activity at follow-up.

Limitations

The most obvious limitation of this retrospective study is that there is bias by indication; the surgeon allocated the patient to the treatment arm at baseline before the study was initiated. This is highlighted by the significant difference between the cohorts with 85% in the surgical treated group having complete proximal hamstring avulsion with at least 2 cm retraction compared with 50% in the non surgical treated group. Since there is no published evidence-based treatment algorithm in the literature indicating on how to treat patients with proximal hamstring avulsion, the treatment decision was based on the orthopaedic surgeon’s experience and local guidelines. The strongest indicators for surgery were MRI finding (Wood type 5 with the tendons avulsed more than 2 cm from the ischial tuberosity), clinical findings and a healthy and active patient. We found a difference at baseline in MRI findings, as there were more patients in the surgically treated group with an MRI result with the tendons avulsed ≥2 cm from the ischial tuberosity than in the non-surgically treated group. This indicates a bias by indication in terms of severity of injury. Thus, cases with a more significant injury and higher activity level were more likely to receive surgical treatment. However, previous published studies also have this problem and are generally case series of surgical treatment.

In addition, there were more females in the non-surgical group and more males allocated to surgical treatment.

LEFS can be a non-specific instrument in patients suffering from a proximal hamstring avulsion. There are studies indicating a risk of the ceiling effect in LEFS.5 12 However, studies have also shown the opposite, recently a systematic review concluded the good reliability, validity and responsiveness of LEFS scores for assessing functional outcomes in patients with various lower musculoskeletal disorders.2 6

The possibility of the ceiling effect was one reason we chose to add several questions from the PHIQ. We found that both groups complain of numbness in their injured leg and that patients in both groups continued to take painkillers for their injured leg.

In the surgical-treated group, patients were training twice as much as in the non-surgical-treated group at our follow-up. As we do not know the physical activity level prior to the injury, it cannot be concluded that there is no difference in physical activity level between the surgically and non-surgically groups.

Interpretation

Considering that this study was performed in a public hospital setting and most of the patients are active middle-aged non-elite athletes, our primary hypothesis was that there would be no differences in LEFS between the two groups at follow-up. The surgical cohort demonstrated a higher severity of injury, with the vast majority of them having complete avulsions with greater than 2 cm of retraction. At t follow-up the surgical cohort were doing physical activity 2.5 hours more than the non-surgical treated cohort. We are aware that this might be a bias by indication. However, we did not find any difference in our primary outcome, LEFS, for surgically treated and non-surgically treated patients. Because the patients in the non-surgical treatment group did not follow any specific physiotherapy protocol, although many physiotherapists in the Stockholm area use the Askling protocol for this injury, we do not know the extent of physiotherapy in this treatment arm. We also do not know if these patients were followed up or if they were left to train by themselves. The non-surgically treated group may thus have scored a higher LEFS result if a comprehensive physiotherapy protocol had been used. Many previous studies describe good results after surgical treatment of proximal hamstring avulsion,13–15 but the problem with many of these studies is that heir instruments are not validated and standardised and that they all lack a control group.

Comparing the results of the validated LEFS in the non-surgically treated cohort of Hofmann et al1 and a surgically treated cohort,7 the scores are similar in both cohorts. The non-surgically treated cohort had 70.2 out of a maximum of 80, and the surgically treated cohort was slightly higher with a mean of 71 out of 80, results that are remarkably consistent with our study. Shambaugh et al2 included 25 patients, with 11 patients in the non-surgical group with a LEFS score of 68.5 (±7.9) and 14 patients in the surgical group with a mean score of 74.7 (±5.4). Notably, the surgically treated patients were, on average, almost 9 years younger (47 vs 55.7 years) in this study.1 2 The LEFS score is also similar to other studies using this validated score with Chahal et al11 reporting LEFS of 75 (±7.8) and Cohen et al10 and Skaara et al7 reporting 75 and 71, respectively, for their patients who underwent surgical treatment. However, all studies have the same problem of bias by indication as with our study.

In the systemic review by van der Made et al,12 the rate of satisfaction with surgery was 88%–100%. Strength ranged in nine studies from 78% to 101% of the uninjured side. From this, most people would be convinced of the benefits of surgery. Interestingly, pain was not uncommon and was reported by 8%–61% of the patients.12 Bodendorfer et al3 summarised the complication rate for the surgically treated patients as high as a 23.7%. The complications described were 2%–3% rerupture, reoperation and infections, 5%–8% incisional numbness and neurological symptoms and 0.68% Venous Tromboembolism (VTE)/Pulmonary Embolism (PE). This indicates surgery is reasonable option for the properly indicated patient, but it is not without risk.

Generalisability

We believe that our results apply to the middle-aged population that we retrospectively reviewed. Retrospective studies are weakened by bias, which likely occurred in this study given the disparity in injury characteristics of the surgical-treated and non-surgical-treated cohorts.