Patients exposed to a surgical safety checklist experience better postoperative outcomes, but this could simply reflect wider quality of care in hospitals where checklist use is routine.

Loss of full knee extension following anterior cruciate ligament (ACL) surgery has been shown to impair knee function.1,2 However, there can be significant difficulties in accurately and reproducibly measuring a fixed flexion of the knee. Some studies suggest that conventional lower limb goniometry may contain errors of between 5 and 10 degrees even in experienced hands.3-5 Such errors may exceed the magnitude of a given fixed flexion deformity. We sought to find a means to eliminate the difficulties associated with palpating the boney landmarks of the femurby making calculations based entirely on the measured position of the tibia. In the setting of state funded healthcare, even a relatively small capital outlay can be prohibitive-we therefore repurposed commercially available technology.We studied the interobserver and the intraobserver reliabilities of our novel, accelerometer based, knee goniometer technique and compared it with a long-armed conventional goniometer for the assessment of fixed flexion knee deformity. Measurements on radiographs would provide a robust "gold standard" but the use of X-ray for this purpose is not routine and not without risk. We therefore chose the best commonly applied "bed-side" measurement technique. Keywords► fixed flexion ► knee ► goniometer ► accelerometer AbstractLoss of full knee extension following anterior cruciate ligament surgery has been shown to impair knee function. However, there can be significant difficulties in accurately and reproducibly measuring a fixed flexion of the knee. We studied the interobserver and the intraobserver reliabilities of a novel, smartphone accelerometer-based, knee goniometer and compared it with a long-armed conventional goniometer for the assessment of fixed flexion knee deformity. Five healthy male volunteers (age range 30 to 40 years) were studied. Measurements of knee flexion angle were made with a telescopic-armed goniometer (Lafayette Instrument, Lafayette, IN) and compared with measurements using the smartphone (iPhone 3GS, Apple Inc., Cupertino, CA) knee goniometer using a novel trigonometric technique based on tibial inclination. Bland-Altman analysis of validity and reliability including statistical analysis of correlation by Pearson's method was undertaken. The iPhone goniometer had an interobserver correlation (r) of 0.994 compared with 0.952 for the Lafayette. The intraobserver correlation was r ¼ 0.982 for the iPhone (compared with 0.927). The datasets from the two instruments correlate closely (r ¼ 0.947) are proportional and have mean difference of only À0.4 degrees (SD 3.86 degrees). The Lafayette goniometer had an intraobserver reliability AE 9.6 degrees. The interobserver reliability was AE 8.4 degrees. By comparison the iPhone had an interobserver reliability AE 2.7 degrees and an intraobserver reliability AE 4.6 degrees. We found the iPhone goniometer to be a reliable tool for the measurement of subtle knee flexion in the clinic setting.

MISS using PPSF is a safe and reproducible technique that maintains or improves functional outcome in the vast majority of patients presenting with spinal metastases.

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