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Occult Hip Fracture: A Clinical & Radiological Correlation

P. Hak , J. Lewis, C. Carpenter, S. Roy, J. Davies.

Departments of Trauma & Orthopaedics, University Hospital of Wales, Heath Park, Cardiff and Royal Glamorgan Hospital, Ynysmaerdy, Llantrisant, Wales.

Address for Correspondence:

Paul Hak.
23 Rowsby Court
CF23 8FG
Phone:  02920 540 348, 07980333737


A prospective, multi-centre study was devised to investigate the correlation between the clinical findings of patients presenting with traumatic hip pain and the presence of occult hip fracture diagnosed on MRI.  32 patients admitted with a suspected occult hip fracture had both hips assessed for evidence of resting limb deformity, point tenderness, hip pain on heel percussion, pistoning and ability to straight leg raise (SLR). Plain radiographs and MRI findings were also recorded in each case and correlated with the findings. 23 out of 32 patients were unable to SLR on the affected side and 21 of those had a fracture of the pelvis or proximal femur on MRI.  9 patients could SLR of which 6 had no fractures and 3 had a fracture of the pelvis or proximal femur on MRI. The results show that the SLR test is 92% sensitive and 75% specific for predicting the presence of a fracture in either the proximal femur or pelvis and is therefore recommended as a simple, reliable test to expedite the investigation, diagnosis and further management of occult hip fractures.

J.Orthopaedics 2009;6(4)e5


Occult hip fracture; straight leg raise; diagnosis hip fracture


Fractures of the femoral neck are relatively common and usually present in the elderly population.  The risk of hip fracture doubles for each decade beyond fifty years of age[1] and is an increasing problem as the population becomes increasingly elderly[2]. The diagnosis is usually made following clinical examination and the use of plain film radiographs. Unfortunately minimally impacted or undisplaced fractures may present with normal or equivocal radiographs especially in the presence of osteoporosis and advanced osteoarthritis[1,3,4,5,6].

There is little in the literature about the clinical findings in patients with occult hip fractures. What has been clearly established is that delayed treatment of hip fractures results in increased morbidity, mortality and hospital stay[7,8,9,10].  Zuckerman showed a ten-fold increase in mortality when the operation was delayed for more than 48 hours after admission[6]. 

The aim of our study was to record the clinical and radiological findings of patients admitted with a suspected neck of femur fracture and to correlate any of the findings with the presence of a fracture on MRI. If a test is shown to be predictive of hip fractures then this can be used to expedite those patients with a suspected hip fracture for further investigation.

Materials and Methods:

A prospective, multi-centre study was conducted looking at all patients admitted with a suspected occult hip fracture that required further investigation. Patients that were noncompliant with examination or had gross degenerative changes of the hip on plain radiographs were excluded. Each patient was assessed for evidence of suspected occult hip fracture and the ability to straight leg raise (SLR). All the patients admitted to the study underwent an MRI scan and the results were correlated with the clinical findings. The SLR test was found to be the most reliable and reproducible test and therefore became the focus of our study.

Results :

32 patients were admitted to the study (10 male and 22 female, age range 58 – 101 years with a mean of 76 years). Of the 32 patients, 23 were unable to straight leg raise on the affected side, 9 were able to do so. Of the 23 patients unable to straight leg raise, 21 had a fracture of the proximal femur and or pelvis on MRI. Of the group of 9 able to straight leg raise 6 had no fracture on MRI and 3 had a fracture to the proximal femur or pelvis. All patients could straight leg raise and had normal MRI of the contra lateral hip.The fractures identified on the MRI scan included: 6 Intertrochanteric, 5 Subcapital, 4 Basicervical, 4 Greater trochanteric, 3 Acetabular , 3 Pubic rami  and 1 Sacral fracture.

Under the conditions of this study the straight leg raise test had a 92% sensitivity and 75% specificity for a fracture of the proximal femur or pelvis.

Diagnosis on MRI


Subcapital fracture






Greater trochanteric


Pubic ramus fracture




Sacral fracture


Discussion :

The straight leg raising test is an accurate and reproducible test to identify those patients with occult hip fracture who need further investigation. This could be due to the fact when actively straight leg raising, the load on the head is estimated to be the same as during the stance phase of the gait cycle (three times body weight) as shown by Rydell[11].

It has been clearly shown in the literature that the mortality and morbidity (thromboembolism, pressure sores, pneumonia) rates for hip fractures rises quickly with increasing delay between admission and eventual treatment[1,5].  Zuckerman showed a three day delay doubled the mortality rate in the first year and noted a ten fold increase in mortality when the operation was delayed for more than forty eight hours following admission[6].  A recent meta-anaylsis of published data found a 41% increase in thirty day all case mortality and an increase of 32% at one year in those whose surgery was delayed greater than 48 hours[10].  Early surgery has also been shown to decrease the length of hospital stay and increase the chances of returning to independent living[7].

Minimally impacted or undisplaced fractures may present with normal or equivocal radiographs especially in the presence of osteoporosis or advanced osteoarthritis[1,5,6].  In these cases further imaging is required. MRI scanning is now the investigation of choice[3,4,12] and has been shown to be 100% sensitive and 100% specific for neck of femur fractures[2].  It is non-invasive, requires no ionizing radiation and the coronal images collected are easier to interpret than a CT scan’s axial images. MRI can also detect subtle changes in bone marrow associated with a fracture and delineate the anatomic configuration of the fracture enabling appropriate surgical planning[4,5,6,8,10,11,13].  Figures 1. & 2. show a neck of femur fracture diagnosed on MRI scan after a normal plain radiograph.

Figure 1: Plain AP pelvic radiograph in a patient with left sided hip pain and inability to SLR.

Figure 2: MRI scan of same patient showing a subcapital fracture of the neck of the left femur.

Cost issues also need to be taken into account when considering the management of patients with a painful hip. The average hospital bed costs 350 per day, a bone scan 60, CT 100 and MRI scan 250. Clearly early diagnosis, investigation and treatment will both reduce the length of hospital stay therefore reducing bed costs as well as improving outcome in terms of mortality, morbidity and a return to independent living[1,5,7,8,9,10].

The straight leg raising test is therefore recommended as a simple, quick and reproducible test to help speed up the diagnosis, investigation and further management of occult fractures of the hip.

Reference :

  1. Ingari JV, Smith DK, Aufdemort TB, Yaszcemski MJ. The anatomic significance of MRI findings in hip fracture. Clin Orthop 1996; 332: 209-214.

  2. Mlinek EJ, Clark KC, Walker CW. Limited magnetic resonance imaging in the diagnosis of occult hip fractures. AJEM 1996;16(4): 390-392.

  3. Chana R, Noorani A, Ashwood N, Chatterji U, Healy J, Baird P.  The Role of MRI in the diagnosis of proximal femoral fractures in the elderly. Injury 2006; 37(2): 185-189.

  4. Hossain M, Barwick C, Sinha AK, Andrew JG.  Is Magnetic resonance imaging (MRI) necessary to exclude occult hip fracture?  Injury 2007; 38(10): 1204-1208.

  5. Pandey R, McNally E, Ali A, Bulstrode C. The role of MRI in the diagnosis of occult hip fractures. Injury 1998; 29(1): 61-63.

  6. Zuckerman JD, Skovron ML, Koval KJ et al. Postoperative complications and mortality rates associated with operative delay in older patients who have a fracture of the hip. J Bone Joint Surg 1995; 77A: 1551-1556

  7. Al-Ani AN, Samuelsson B, Tidermark J, Norling A, Ekstrom W, Cederhol T, Hedstrom M.  Early operation on patients with a hip fracture improved the ability to return to independent living.  A prospective study of 850 patients.  J Bone Joint Surg (Am) 2008; 90(7): 1436-1442.

  8. Hommel A, Ulander K, Bjorkelund KB, Norrman PO, Wingstrand H, Thorngren KG. Influence of optimized treatment of people with hip fracture on time to operation, length of hospital stay, reoperations and mortality within 1 year.  Injury 2008; 39(10): 1164-1174.

  9. Novak V, Jotkowitz A, Etzion O, Porath A.  Does delay in surgery after hip fracture lead to worse outcomes?  A multicenter survey.  Int J Qual Heath Care 2007;   19(3): 170-176.

  10. Shiga T, Wajima Z, Ohe Y.  Is operative delay associated with increased mortality of hip fracture patients?  Systematic review, meta-analysis, and meta-regression.  Can J Anaesth 2008; 55(3): 146-154.

  11. Rydell N. Biomechanics of the hip joint. Clin Orthop 1973; 92: 6-15.

  12. Frihagen F, Nordsletten L, Tariq R, Madsen JE.  MRI diagnosis of occult hip fracture.  Acta Orthop 2005; 76(4): 524-530.

  13. Rizzo PF, Gould ES, Lyden JP, Asnis SE. Diagnosis of occult fractures about the hip. J Bone Joint Surg (Am) 1993; 75: 395-401

This is a peer reviewed paper 

Please cite as: Paul Hak: Occult Hip Fracture: A Clinical & Radiological Correlation.

J.Orthopaedics 2009;6(4)e5





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