Validity of goniometric elbow measurements: comparative study with a radiographic method

Abstract

Background: A universal goniometer is commonly used to measure the elbow's ROM and carrying angle; however, some authors question its poor intertester reliability.

Questions/purposes: We (1) assessed the validity of goniometric measurements as compared with radiographic measurements in the evaluation of ROM of the elbow and (2) determined the reliability of both.

Methods: The ROM and carrying angle of 51 healthy subjects (102 elbows) were measured using two methods: with a universal goniometer by one observer three times and on radiographs by two independent examiners. Paired t-test and Pearson's correlation were used to compare and detect the relationship between mean ROM. The maximal error was calculated according to the Bland and Altman method.

Results: The intraclass correlation coefficients (ICC) ranged from 0.945 to 0.973 for the goniometric measurements and from 0.980 to 0.991 for the radiographic measurements. The two methods correlated when measuring the total ROM in flexion and extension. The maximal errors of the goniometric measurement were 10.3° for extension, 7.0° for flexion, and 6.5° for carrying angle 95% of the time. We observed differences for maximum flexion, maximal extension, and carrying angle between the methods.

Conclusion: Both measurement methods differ but they correlate. When measured with a goniometer, the elbow ROM shows a maximal error of approximately 10°.

Clinical relevance: The goniometer is a reasonable and simple clinical tool, but for research protocols, we suggest using the radiographic method because of the higher level of precision required.

Fig. 1A–C

The landmarks for (A) extension and (B) flexion are the lateral epicondyle, tip of the acromion, and midline of the wrist. (C) The instrument was centered on the crossline of the biceps tendon and the interepicondyle axis for the carrying angle measurement.

Fig. 2A–C

Landmarks are the same for (A) extension and (B) flexion. The average humeral diaphysis axis and dorsal midthird edge of the ulna defines the angle of flexion. Measurement of the (C) carrying angle is complicated by the S shape of the ulna. The reference portions were the ulnar segment between the radial head and radial tuberosity and the farthest distal diaphysis segment on the radiograph.

Fig. 3A–D

In each diagram, the points (n = 102, both elbows of the 51 participants) represent the difference between both measurement methods (radiographs or goniometer) against the mean values in degrees. The middle line represents the mean difference, whereas the upper and lower lines indicate the 95% CI. For (A) extension, 95% of UG measurements were ± 10.3° from radiographic values. Similarly, the UG maximal error was (B) ± 7.0° for flexion, (C) ± 11.5° for total ROM, and (D) ± 6.5° for carrying angle. RX = radiographic; UG = universal goniometer.