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Case Discussion: Syndesmosis Injury with a Normal MRI in a 15yo Girl Complicated by CRPS

Miss B is a 16 year old girl who was referred to Dr Touzell via her physiotherapist and General Practitioner. Miss B sustained an inversion injury of her right ankle in May 2019 which failed to improve despite a comprehensive rehabilitation program with an experienced sports physiotherapist.

Her rehabilitation program prior to her review included calf strengthening, proprioception exercises and range of motion exercises. She continued to have intermitted pain and instability and was unable to play netball.

On examination, Miss B demonstrated signs concerning for Complex Regional Pain Syndrome (CRPS) and she met the Budapest Criteria for CRPS diagnosis (Bullen 2016, see below). She also clinically had an unstable ankle and moderate tenderness at the syndesmosis.

Due to her CRPS symptoms, she was commenced on vitamin C 500mg for fifty days and referred back to her allied health practitioner for desensitisation, mirror therapy and range of motion exercises. It was determined that surgery was inappropriate at that stage due to the risk of exacerbating her CRPS. In addition, both 1.5T and 3T MRI scans did not demonstrate any injury to the syndesmosis and only a partial tear to the anterior talo-fibular ligament was identified with no other pathology, so both Dr Touzell and Miss B were reluctant to proceed with surgery.

Miss B's CRPS symptoms resolved over the ensuing six months, but her pain and instability continued. It was therefore decided to proceed with an ankle arthroscopy and lateral ligament stabilisation. On direct visual inspection arthroscopically, the syndesmosis was clearly unstable with a positive 'push through' sign where an arthroscopic probe and shaver can enter the distal tibio-fibula joint confirming instability. In addition, on inspection of the lateral ligaments the anterior talo-fibular ligament (ATFL) was clearly ruptured while the calcaneo-fibular ligament (CFL) was intact. Dr Touzell therefore proceeded with a brostrom-type reconstruction of the ATFL and stabilisation of the syndesmosis (see figure 1).

X-ray image

Miss B's post-operative course was uncomplicated, and she was prophylactically prescribed vitamin C post-operatively. She commenced a standard post-operative ankle rehabilitation program with her physiotherapist two weeks after surgery as per our standard post-operative rehabilitation protocol (see below). Six months after surgery, she is back running and her pain has completely resolved. She did not develop CRPS post-operatively. She is optimistic about recommencing netball when school sport recommences.

This is a really interesting case for several reasons. Miss B's MRI scan did not report a syndesmosis injury and the partial tear of her ATFL did not correlate to direct inspection or clinical examination which demonstrated a complete rupture and significant ankle instability. In addition, Miss B initially had symptoms on her first presentation consistent with CRPS which responded well to allied health intervention and vitamin C therapy prior to surgery.

Key Learning Points:

  • CRPS is a known post-injury complication in any age group.

  • Vitamin C 500mg daily for fifty days appearrs to be a safe, cost-effective adjunct treatment for patients with suspected CRPS when combined with a multidisciplinary approach to management.

  • If a patient with ankle pain and instability has a normal MRI scan, careful clinical correlation is warranted to exclude unreported ligament injury. Orthopaedic referral is appropriate for a patient with ankle pain and/or instability, even in the setting of a normal MRI.

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