What looks like a hamstring tear could be an avulsion fracture in sporty youngsters. Elizabeth Ashby and Fares Haddad explain
Avulsion fracture of the ischial tuberosity is a rare condition that mainly affects athletes between 15 and 25 years old. The fracture is commonly misdiagnosed as a soft tissue hamstring injury, which leads to inappropriate treatment, resulting in chronic pain and malfunction.
A 15-year-old boy presented to the accident and emergency department with pain in his left buttock after a rugby injury. The mechanism of injury was unclear. Examination of the left hip revealed no obvious swelling or deformity. He was tender over the left ischial tuberosity and had a full range of motion in the hip. He was able to walk but unable to run. He had a pelvic x-ray, which was misreported as showing no bony abnormalities.
The young rugby player was referred for physiotherapy for a presumed soft tissue hamstring injury. He continued his physio for six months but made poor progress, so he was referred to an orthopaedic surgeon. He had another pelvic x-ray and a hip ultra- sound scan. Both showed a displaced ischial tuberosity avulsion fracture. Conservative management was continued for a further year; yet despite a structured physio programme, he remained unable to run and therefore unable to return to sport.
Eighteen months after the initial injury he was referred to a sports orthopaedic surgeon. A CT scan of the pelvis showed an ischial tuberosity avulsion fracture with 2.5cm displacement. An ultrasound scan showed the torn-off fragment of bone to be mobile. Since conservative management had thus far been unsuccessful, we decided to operate to close up and fix the fracture. The patient returned to full active contact sport within six months.
Each side of the pelvis is composed of three bones: the ischium, ileum and pubis. The ischium is the lowest and strongest part of the pelvis. It is attached to the pubis at the front and the ileum at the back. The upper edge of the ischium is in the centre of the acetabulum (hip socket). The lowest point of the ischium is the ischial tuberosity, which is palpable as a bony prominence in the buttock and is used for sitting (the sit bones). The ischial tuberosity provides the origin for all three hamstring muscles (biceps femoris, semitendinosus and semimembranosus) and for adductor magnus.
Fracture of the ischial tuberosity
Ischial tuberosity avulsion fractures occur through the apophysis. This apophysis (secondary ossification centre) appears at puberty and fuses into hard bone in late adolescence. So most ischial tuberosity avulsion fractures occur in young sportsmen and women between the ages of 15 and 25. The highest incidence is among 15 to 17 year olds.
The apophysis of the ischial tuberosity is weaker than the hamstring tendons and muscles. If a large force is put across the hamstrings when the apophysis is open, it is more likely to result in an avulsion fracture of the ischial tuberosity than a hamstring soft tissue injury. After adolescence, when the apophysis has fused, hamstring soft tissue injuries are more likely than an ischial tuberosity avulsion fracture, since the ischial tuberosity is no longer the weakest link in the chain.
Mechanism of injury
Ischial tuberosity avulsion fractures occur as a result of sudden forceful hamstring contractions or stretching (the latter occurs when the hip is excessively flexed with the knee in full extension). Among athletes the injury is most commonly seen in soccer players and gymnasts(1), although fractures also occur in sprinters, long-jumpers and hurdlers.
The athlete usually presents with buttock or groin pain, which can be severe. Sitting may be particularly painful. The patient often has difficulty walking and is unable to run. Because avulsion fractures are often misdiagnosed initially as soft tissue injuries, the patient may present only by the time there is chronic pain and disability.
On examination there may be swelling over the fracture site, and the ischial tuberosity will be tender to touch. The hamstrings are weak but there is often a full range of movement in the hip.
The differential diagnosis includes:
* hamstring muscle or tendon tear
* piriformis syndrome
* vertebral disc prolapse
* ischial tuberosity bursitis
It is often difficult to distinguish between an avulsion fracture and a hamstring soft tissue injury, but important clues that suggest an avulsion fracture include the athlete’s age and an inability to weight-bear.
A pelvic x-ray should be performed in all patients with ischial tuberosity tenderness and in those who cannot weight-bear. If a fracture is seen, a CT scan will further delineate the fracture and give an accurate measurement of the distance between the fracture fragment and the pelvis. If no fracture is seen on x-ray, an MRI scan should be considered to assess whether there is a soft tissue injury needing surgical repair.
Ischial tuberosity avulsion fractures may be treated conservatively or operatively. An absolute indication for surgery is disturbance of the sciatic nerve. Other indications include more than 2cm displacement of the avulsion fragment(2), persistent pain in a non-union (where the bone does not knit) and in athletes who are unable to regain full function. Surgical treatment is recommended for all elite athletes who do not make a significant improvement after one month of conservative management(3,5).
Conservative treatment involves a struc- tured programme of physiotherapy rehabilitation. The first aim will be to control pain with ice, rest and non-steroidal anti-inflammatory drugs and to re-establish a normal gait using weight shifts and single-leg stance balancing. The patient can then begin exercises to improve hip range of motion, hip strength and neuromuscular coordination. Once the athlete has achieved full strength and range of motion, they will be ready for progressive cardiovascular endurance and functional exercises in preparation for their return to full training.
The main benefit of conservative treat- ment is that it avoids surgical complications such as infection and nerve damage. However, conservative management does bring its own complications, the most common of which is non-union (failure of the bone to bind) at the fracture site. This causes chronic pain and malfunction. A further possible complication is ‘hamstring syndrome’, in which the hamstring origin shortens and fibroses, again leading to pain and disability.
There are two options for surgical treat- ment:
* resection (cutting away) of the loose fragment
* open reduction and internal fixation of the fragment (joining the bone back together and pinning it).
The advantage of resection is that it is a simpler and quicker procedure. The main disadvantage is that an osteoma (a mass of bone) may form post-operatively which then requires clinical and radiological follow-up. The advantage of open reduction and internal fixation is that normal anatomy is restored with a good functional outcome(4). The standard operative risks apply to both types of surgery but for elite athletes, most authors recommend open reduction and internal fixation, as it is likely to offer a quicker return to full fitness.
Avulsion of the ischial tuberosity is a rare injury which tends to be missed. It should be considered in any young athlete with buttock pain, tenderness over the ischial tuberosity or difficulty weight-bearing. A pelvic x-ray will confirm the diagnosis. Treatment is either conservative or operative. Open reduction and internal fixation is recommended for all elite athletes who do not significantly improve with one month of conservative treatment.
1. Rossi F, Dragoni S (2001) ‘Acute avulsion fractures of the pelvis in adolescent competitive athletes: prevalence, location and sports distribution of 203 cases collected’. Skeletal Radiol. Mar; 30(3): 127-31.
2. Kaneyama S, Yoshida K, et al (2006) ‘A surgical approach for an avulsion of the ischial tuberosity: a case report’. J Orthop Trauma. May; 20(5): 363-5.
3.Bolgla LA, Jones DL et al (2001) ‘Hip pain in a high school football player: a case report’. J Athl Train, Jan-Mar; 36(1): 81-84.
4. Gidwani S, Jagiello J & Bircher M (2004) ‘Avulsion fracture of the ischial tuberosity in adolescents – an easily missed diagnosis’. BMJ, 329; 99-100.
5. Salvi AE, Metelli GP et al (2006) ‘Spontaneous healing of an avulsed ischial tuberosity in a young football player. A case report’. Acta Orthop Belg, Apr; 72(2): 223-5.