215 J. St. Marianna Univ. Original Article Vol. 6, pp. 215–224, 2015 Anatomical Study of the Contact Area and Degenerative Change of the Proximal Radioulnar Joint During Forearm Rotation Satoshi Nishimura1, Masahiro Tanaka1, Takeshi Arai1, Hisateru Niki1, and Kazuaki Hirata2 (Received for Publication: August 20, 2015) Abstract Although the articular circumference of the radial head is known to affect lateral stability of the elbow joint, no studies have reported an association between the radial head and radial notch of the ulna, which form the joint. The objective of this study was to investigate, from an anatomical perspective, the association of con‐ tact between the radial head and radial notch of the ulna in the proximal radioulnar joint (PRUJ) with develop‐ ment of cartilage injury during pronation and supination of the forearm. Forty-nine elbows from 26 cadavers were included for systemic anatomical study. After the articular circumference of the radial head and the radial notch of the ulna were divided into 4 and 9 regions, respectively, the presence or absence and severity of carti‐ lage injury were determined. The contact area between the radial head and radial notch of the ulna was 50% smaller with the forearm at the pronated position than at the supinated position. Cartilage injury was observed in the medial region of the articular circumference of the radial head and the distal regions of the radial notch of the ulna. These regions corresponded to the contact area of the PRUJ with the elbow joint extended and the forearm pronated. In this condition, the elbow joint becomes most unstable. The elbow joint lateral support complex is likely to be impinged in the humeroradial joint with the elbow joint extended and the forearm prona‐ ted, suggesting that repeated impingement might induce cartilage injury. Key words proximal radioulnar joint, forearm rotation, elbow joint lateral support complex, cartilage injury, refractory lateral humeral epicondylitis and cartilage injury of the radial head5). However, the Introduction association between those findings and the pathology The pathology underlying lateral humeral epi‐ of refractory lateral humeral epicondylitis has still condylitis is classically considered to involve enthesi‐ not been elucidated. tis at the origin of the forearm extensor tendon1) or The synovial fold forms a single complex be‐ enthesopathy2). Conservative treatment provides relief tween the enthesis of the extensor carpi radialis bre‐ in most cases3). Although surgery has often been per‐ vis and the joint capsule6)7). Tanaka et al.8) reported formed in cases resistant to treatment2), there have re‐ that this elbow joint lateral support complex in the cently been sporadic reports of arthroscopic surgery4). humeroradial joint was impinged as a mass during The reported arthroscopic findings in refractory cases forearm pronation, that the location of the synovial include lateral rupture of the humeroradial joint cap‐ fold corresponded to the site of cartilage injury of the sule, degeneration of the enthesis of the extensor radial head, and that cartilage injury of the radial carpi radialis brevis, synovial fold injury, synovitis, head was severe where the radial head contacted the 1 Department of Orthopaedic Surgery, St. Marianna University School of Medicine 2 Department of Anatomy, St. Marianna University School of Medicine 113 216 Nishimura S Tanaka M et al synovial fold during forearm pronation. According to capsule was longitudinally incised on the median line these findings, cartilage injury is likely to occur at the along the radial axis. soft tissue and bony aspects of the radial head during forearm pronation, and the pathology of refractory 4. Transection of bone lateral humeral epicondylitis may cause early The following parts were transected vertically to changes resulting in concomitant osteoarthritis of the the axis of the bone with a saw. In the central part, elbow joint8)9). the humeral diaphysis was transected 10 cm from the The objectives of this study, according to macro‐ capitulum of the humerus in the humeroradial joint. scopic anatomical findings, were 1) to observe the In the peripheral part, the radial neck and the proxi‐ contact area between the radial head and radial notch mal ulnar diaphysis were transected 10 cm from the of the ulna with the forearm pronated and supinated, surface of the radial head in the humeroradial joint. 2) to determine the sites and severity of cartilage in‐ The joint capsule was resected at the humeral enthe‐ jury in the proximal radioulnar joint (PRUJ), and 3) sis and turned over (Figure 1). to discuss osteoarthritis of the PRUJ in terms of the pathology of refractory lateral humeral epicondylitis. Study parameters The following 4 parameters were examined. Materials and Methods An electronic caliper manufactured by Mitsu‐ This systemic anatomic study included 49 el‐ toyo (Digimatic Caliper CD-10 CX; Mitsutoyo, Ka‐ bows from 26 cadavers. Sixteen elbows from 8 male wasaki, Japan) was used to measure all parameters. cadavers (8 right elbows and 8 left elbows) and 33 el‐ Each parameter was measured 3 times by the same bows from 18 female cadavers (16 right elbows and examiners. Then, mean values and standard devia‐ 17 left elbows) were included. Mean age of the pa‐ tions of the measurements were calculated. tients at the time of death was 86 years (range, 75–96 years). Although it was unknown whether these per‐ 1. Morphology of the radial notch of the ulna sons had a history of trauma or complaints before After the joint capsule was resected from the ra‐ death, cadavers with apparent traumatic changes were dial notch of the ulna, the length (L), depth (D), and excluded. Further, this study included only cadavers height (H) of the articular surface of the radial notch in which the forearms could be kept at 90° pronation of the ulna were measured. Both length and depth and supination with the elbow joints at 0° extension after manipulation of the elbow joints. In this study, “pronation” was used to classify a pronation of 90°, and “supination” was used to classify a supination of 90°. This study was approved by the ethics commit‐ tee at St. Marianna University School of Medicine (approval no. 2787). Dissection procedure and methods 1. Exposure of the superficial layer With the elbow joint extended and the forearm pronated, the lateral side of the elbow joint was ex‐ posed to identify the extensors of the forearm. 2. Exposure of soft tissue The extensors of the forearm were excised, but Figure 1. The humeroradial joint. the joint capsule, annular ligament, and interosseous The anterior aspect of the humerora‐ membrane were not excised. dial joint capsule was longitudinally incised on the median line along the 3. Exposure of the humeroradial joint radial axis with the elbow joint ex‐ The anterior aspect of the humeroradial joint tended and the forearm pronated. 114 Anatomical study of the PRUJ 217 Figure 2. Morphology of the radial notch of the ulna. Length (L) · Depth (D) · Height (H) measurements for evaluating shape of the ulnar radial notch joint surface. The ulnar radial notch depth and the joint surface length are measured at the proximal, middle, and distal levels. (a) Axial CT image at the level of proximal radioulnar joint. (b) 3D CT image of the articular surface of the radial notch of the ulna. (c) Anatomy of the articular surface of the radial notch of the ulna. L: the longitudinal direction of the joint surface length of the ulnar radial notch, D: the maximum depth on each joint face length, H: the maxi‐ mum value of the distance to the distal articular surface of the perpendicular line from the proximal articular surface. were measured at the proximal, medial, and distal points (Figure 2). 2. Distribution and severity of cartilage injury in the radial notch of the ulna The articular surface of the radial notch of the ulna was divided into the following 9 regions: proxi‐ mal-anterior (pa) region, proximal-posterior (pp) re‐ gion, distal-anterior (da) region, distal-posterior (dp) region, regions between them (pa+pp, pa+da, pp+dp, and da+dp), and central region (O). The distribution and severity of cartilage injury examined are indica‐ ted in Figure 3. The severity of cartilage injury was classified into the following 5 grades according to the Interna‐ tional Cartilage Repair Society (ICRS) classifica‐ 10) tion : Grade 0, normal; Grade 1, softening and fis‐ Figure 3. Evaluation of articular cartilage in the ulnar ra‐ sure of cartilage; Grade 2, cartilage defect of less dial notch. than 50%; Grade 3, cartilage defect of more than The articular surface of the radial notch of the 50% ; and Grade 4, defect extending to the subcarti‐ ulna was divided into 9 regions. The severity of laginous bone. In this study, severe cartilage injury cartilage injury was classified according to the was classified as Grade 3 or 4, and the number of ICRS classification. pp: proximal · posterior, pa: such injuries was calculated. proximal · anterior, da: distal · anterior, dp: dis‐ tal · posterior, O: central, ante.: anterior, dist.: 3. Distribution and severity of cartilage injury in distal, post.: posterior, prox.: proximal. the articular circumference of the radial head When the anterior median axis at the articular circumference of the radial head at the pronated posi‐ 115 218 Nishimura S Tanaka M et al tion was set as 0°, a region ranging from −45° to 45° was defined as the anterior (A) region. The subse‐ quent area was divided every 90° in the ulnar direc‐ tion into the following 3 regions: medial (M), poste‐ rior (P), and lateral (L). The distribution and severity of cartilage injury were examined in these A, M, P, and L regions (Figure 4). The severity of cartilage injury was classified according to the ICRS system,10) as was the radial notch of the ulna.