Weight-Bearing Test: A Straightforward and Reliable Indicator of Stability in Supination-External Rotation Type, Weber B Ankle Fractures

Abstract

Background

Surgical indications of supination-external rotation type, Weber B (SER/Weber B) ankle fractures seem to be well defined according to the stability of the mortise. However, in some SER type lateral malleolar fractures with suspicious medial clear space widening, it is not easy to determine their stability. Clinical signs and other tests have been proposed to differentiate the stability of those fractures; however, these methods seem to have major concerns and limitations. Therefore, we adopted the weight-bearing (WB) test as a simple and predictable test and report the outcomes of the SER/Weber B type lateral malleolar fractures treated nonoperatively based on the WB test.

Methods

In patients with SER/Weber B lateral malleolar fractures without a definite sign of medial clear space widening, the WB test was performed to assess fracture stability. If the patients with SER type lateral malleolar fractures were able to stand and walk at least 4 steps without any walking aid, fractures were considered stable and nonoperative treatment was selected. Seventy-nine Weber B lateral malleolar fractures were managed nonoperatively. Among them, 68 patients were followed up for more than 6 months. Radiographic parameters, the visual analog scale (VAS) pain score, and the American Orthopaedic Foot and Ankle Society (AOFAS) ankle-hindfoot score were evaluated and analyzed.

Results

Radiographic union was achieved in all 68 patients for whom the congruency of the joint was maintained through the last follow-up without any problems. The average VAS score was 1.03 (range, 0–5) and the mean AOFAS score was 87.34 (range, 58–100). All patients returned to their pre-injury level of daily activities.

Conclusions

Based on these good radiographic and clinical outcomes, the WB test appears to be a simple and reliable clinical indicator for identifying stable SER/Weber B type lateral malleolar fractures that can be managed nonoperatively.

Ankle fractures account for 10.2% of all fractures, with the supination-external rotation type, Weber B (SER/Weber B) pattern representing up to 85% of these ankle fractures.¹⁾ In treating these fractures, the surgical indications based on the stability of the mortise are well established.²,³,⁴,⁵,⁶⁾ However, in clinical practice, the challenge in treating isolated lateral malleolar fractures of the SER/Weber B type lies in the difficulty of clinically and radiographically distinguishing SER-II injuries from SER-IV equivalent injuries. Due to the difficulty in distinguishing between the 2, numerous methods have been employed. Clinical signs such as ecchymosis, swelling, and tenderness are used, as well as radiographic tests like the external rotation (ER) stress test, gravity stress test, and weight-bearing (WB) radiography.⁷,⁸,⁹⁾ Recently, ultrasonography and magnetic resonance imaging (MRI) have also been utilized for this purpose.¹⁰,¹¹,¹²⁾ However, considering the reliability and cost aspects of the tests, the ER stress test, gravity stress test, and WB radiography are still widely used today to assess the stability of the mortise. Nonetheless, these tests can yield different results depending on the patient’s position and the imaging technique. Moreover, they can cause significant pain and discomfort for patients with fractures and require considerable effort from the examiner. Additionally, it has been suggested that the ER stress test and gravity stress test, being artificial tests, do not reflect the physiological mechanics of a person standing or walking normally and may overestimate mortise instability.¹³,¹⁴⁾ Therefore, we aimed to introduce a simple, painless outpatient method to assess mortise stability. We concluded that the ability to bear weight and walk is a reliable indicator of the stability of the ankle joint, which we termed the WB test. Since 2016, we have used the WB test to evaluate the stability of SER/Weber B isolated lateral malleolar fractures and have performed nonoperative treatment for patients who pass the test. Here, we present the results.

METHODS

This study was approved by the Institutional Review Board of Samsung Medical Center (IRB No. 2024-07-064). The Institutional Review Board granted a waiver of informed consent because the study involved minimal risk, relied solely on standard clinical care, and used anonymized retrospective data.

We conducted a cohort study to evaluate the ability of the WB test to assess the stability of the mortise in cases of SER/Weber B lateral malleolar fractures. According to previous research, medial clear space (MCS) widening> 5 mm is considered indicative of an unstable ankle fracture; therefore, patients with values exceeding this threshold were excluded from the present study.¹⁵⁾ Since 2016, we included patients aged 19–80 years with acute SER/Weber B lateral malleolar fractures within 2 weeks of injury who were referred to our foot and ankle clinic from our emergency department or external hospitals. Among these patients, those with an MCS > 5 mm on non-WB radiographs were considered to have obvious mortise instability and underwent surgical treatment. For patients with an MCS ≤ 5 mm, a WB test was performed. If they passed the test, nonoperative treatment was administered. The WB test we conducted required patients to remove any braces or casts they were wearing. Patients were considered to have passed the test if they could stand in place without any walking aids and walk at least 4 steps on their own. The exclusion criteria included preexisting gait disturbance due to medical illness, neuromuscular diseases, Charcot joint, and peripheral arterial occlusive disease. Between 2016 and December 2023, a total of 79 patients passed the WB test and underwent nonoperative treatment. Among them, 68 patients were followed up for more than 6 months (Fig. 1).

Fig. 1. Flowchart of patient inclusion. SER/Weber B: supination-external rotation type, Weber B, MCS: medial clear space widening.

Our nonoperative treatment comprised a short leg walking cast for < 3 weeks and a walking boot for another 6 weeks allowing tolerable WB, range of motion, and strengthening exercise. The primary outcome measures were radiographic bony union and joint congruency. The secondary outcome measures included the visual analog scale (VAS) pain score and the American Orthopaedic Foot and Ankle Society (AOFAS) ankle-hindfoot score. Radiographic bony union was defined as a visible fracture line < 50% of the original fracture lines or evidence of callus formation on follow-up radiographs taken 6 months after injury, with only cases where 2 orthopedic specialists (MS and YL) reached consensus included in the analysis. Joint congruency was verified using the same method. The VAS pain score and AOFAS score were assessed starting 6 months after the initiation of nonoperative treatment, and the results from the last visit were used for analysis.

For statistical analysis, this study was designed as a single-arm, result-demonstration cohort without a comparison group. Therefore, formal hypothesis testing was not required. Descriptive statistics were used to summarize radiographic outcomes, pain scores, and functional measures. Continuous variables were reported as means and ranges. All statistical analyses were performed using R software version 4.4.0 (R Foundation for Statistical Computing).

RESULTS

The cohort study included 68 patients, with 22 men and 46 women. The average age was 57.9 years (range, 22–80 years), and the average follow-up period was 10 months (range, 6–34 months). It took an average of 4.26 days for patients to visit our clinic for the first time after injury. The average MCS on the non-WB radiograph taken at the time of injury was 3.86 mm (range, 2.3–5 mm). Radiographic union was achieved in all 68 cases for whom the congruency of the joint was maintained through the last follow-up without any evidence of posttraumatic arthritis. Additionally, no other significant findings, such as osteoarthritis, were observed. The clinical outcomes were measured at the time of the last visit. The average VAS score was 1.03 (range, 0–5) and the AOFAS score was 87.34 (range, 58–100). All patients returned to their pre-injury levels of daily activities. A representative case is illustrated. A 61-year-old man visited the clinic on the seventh day after the injury. Initial non-WB radiographs showed widening of the MCS (Fig. 2). However, a WB test was performed, and the patient passed, allowing for nonoperative treatment. At the 10-month follow-up, he was pain-free, and radiographs confirmed bone union and well-maintained mortise space (Fig. 3).

Fig. 2. Initial non-weight-bearing radiography. (A) Ankle mortise view. (B) Ankle lateral view.

Fig. 3. Six-month follow-up weight-bearing (WB) radiography. (A) Ankle anteroposterior view. (B) Ankle lateral view.

DISCUSSION

In treating ankle fracture patients, protocols based on stability are well-known to yield predictable and mostly good-to-excellent long-term outcomes. However, there is still much debate regarding the methods for assessing stability. As a result, the treatment of ankle fractures is often left to the discretion of the physician, leading to many cases where unnecessary surgical treatment is performed. In fact, in our cohort study, many patients with an MCS ≤ 5 mm were recommended for surgical treatment at external hospitals. However, we administered nonoperative treatment, and all patients recovered well. Our study aimed to establish a reliable and straightforward method for assessing the stability of SER/Weber B lateral malleolar fractures in the clinical setting without conducting numerous costly and time-consuming tests. The idea originated from clinical observations that some fracture patients could ambulate early, supporting the hypothesis that preserved deep deltoid integrity allows safe WB. Although no prior study has validated this exact method, WB radiographs have been used similarly to assess fracture stability.¹³⁾ This clinical rationale forms the basis of the originality and relevance of our approach. Additionally, our goal was to replace tests that cause significant discomfort and pain to patients, such as the widely used ER stress test and gravity stress test, which are known for their high diagnostic value.¹⁶,¹⁷⁾ In this context, the WB test we conducted was performed in the clinic with 2 medical staff standing on either side of the patient, ready to assist if necessary. In all cases, patients did not report significant pain or discomfort during the WB test. In our study conducted in this manner, we obtained satisfactory results in all 68 patients. Moreover, even patients who were not included in the cohort study due to a short follow-up period were able to walk without braces and return to their daily lives after 2–3 months of nonoperative treatment.

This study has several limitations. First, the sample size was relatively small and no direct comparison group was included; therefore, the findings do not determine which assessment method is most appropriate for selecting nonoperative management. Instead, the results suggest that isolated Weber B/SER type fractures that tolerate WB may be safely treated nonoperatively. Second, interobserver variability in MCS measurement was not assessed, which may influence stability classification near the cutoff value. Third, validated patient-reported outcome measures such as the Foot and Ankle Outcome Score or 36-Item Short Form Survey were not collected, limiting the evaluation of functional outcomes. Fourth, the follow-up period was relatively short and insufficient to evaluate long-term complications such as posttraumatic arthritis or late instability. Finally, because this was a single-center study limited to patients able to undergo early WB testing, the generalizability of these findings to patients with delayed presentation, polytrauma, or different healthcare settings remains limited.

Based on these good clinical and radiographic results, we believe we have proposed a reliable and straightforward method for assessing stability that does not cause discomfort and pain to patients. This method can be used in ambiguous situations when deciding treatment for patients with SER/Weber B isolated lateral malleolar fractures, where differentiation between SER-II and SER-IV equivalents is required.