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Articular cartilage injuries of the capitellum interposed in radial head fractures: A report of ten cases
Articular cartilage injuries of the capitellum interposed in radial head fractures: A report of ten cases Andrew E. Caputo, MD, Kevin J. Burton, MD, Mark S. Cohen, MD, and Graham J. King, MD, Hartford, CT
Ten cases of Mason type I and type II isolated radial head fractures are reported, in which an unexpected cartilaginous fragment of the capitellum trapped within the radial head fracture was identified at the time of surgery. In no case was this injury pattern identified on preoperative imaging, including computed tomography in 2 cases. Five patients did have preoperative mechanical findings with forearm rotation. At surgery, all capitellar fragments were found to originate from the posterolateral capitellum. Excision of the capitellar fragment and internal fixation of the radial head fracture were performed in all cases. No sequelae were identified on short-term follow-up. This series highlights an injury pattern that should be considered in isolated nondisplaced and minimally displaced fractures of the radial head. The natural history of this finding, when treated conservatively, is unknown. (J Shoulder Elbow Surg 2006;15:716-720.)
three different surgeons (A.E.C., M.S.C., and G.J.K.). Relative to the total number of operatively treated radial head fractures during the study period, this represents 2 of 26 over a 2-year period (G.J.K.), 3 of 37 over a 3-year period (M.S.C.), and 5 of 55 over a 3-year period (A.E.C.). None of the patients had concomitant soft-tissue or bony injuries of the elbow or upper extremity. Intraoperatively, in all cases, there was an unexpected shear fracture of the capitellar articular cartilage wedged into the radial head fracture blocking reduction. The mean patient age was 33 years, with a range of 18 to 50 years. A retrospective evaluation of the cases was performed. All original radiographs were evaluated in an effort to determine fracture characteristics of this injury complex. Fractures were categorized by the classification of Mason.10 Operative findings were recorded. Collateral ligament insufficiency was assessed by gross observation and, if necessary, intraoperative fluoroscopic stress examination. A final follow-up assessment of function, pain, and fracture healing was performed to determine clinical outcome.
R adial head fractures are the most common frac-
RESULTS
tures of the elbow and have a variety of associated injuries. One of the less recognized, but intuitively obvious of these, is trauma to the capitellum. For fracture to occur, the radial head must be compressed against the humeral capitellum,14 and concomitant radial head and capitellar fractures have been described.5-7,11-13,17 The purpose of this article is to describe 10 unusual cases of radial head fractures in which a cartilage fragment from the posterolateral capitellum was vertically interposed directly into the radial head fracture. Reduction of the radial head fracture was not possible without removal of this cartilaginous fragment. MATERIALS AND METHODS Ten patients underwent open reduction–internal fixation of seemingly isolated displaced radial head fractures by From the Orthopaedic Associates of Hartford. Reprint requests: Andrew E. Caputo, MD, Orthopaedic Associates of Hartford, 85 Seymour St, Suite 607, Hartford, CT 06106. Copyright © 2006 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/2006/$32.00 doi:10.1016/j.jse.2006.01.007
716
The mechanism of injury in all patients was a fall on the outstretched upper extremity. Of the 10 radial head fractures, 9 were Mason type II and 1 was type I. In 5 cases, the decision to operate was, in part, based on limited or painful forearm rotation accompanied by crepitus. In the minimally displaced (type I) case, radiocapitellar crepitus and rotation loss were present despite an intraarticular injection of lidocaine. In the other 5 cases, the decision to proceed with operative fixation was based on the displacement of the radial head fracture and the age and activity level of the patients. Preoperative radiographs did not delineate the capitellar injury in any case. Two patients had preoperative computed tomography scans with 3-dimensional reconstruction. These studies also did not reveal an injury to the capitellum. All patients underwent open reduction–internal fixation of the radial head fragment. At the time of operation, all cases had an unexpected fragment of articular cartilage interposed vertically within the fracture site. Further inspection revealed an articular cartilage defect on the posterolateral aspect of the capitellum. All of the capitellar fragments were relatively small, ranging from 3 ⫻ 5 mm to 10 ⫻ 10 mm. None
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J Shoulder Elbow Surg Volume 15, Number 6
of the capitellar fragments was considered large enough to support stable internal fixation, and therefore, they were excised in all cases. The only treatment for the defect in the capitellum was debridement of loose edges, and specifically, no microfracture techniques were used. In no case was associated intraarticular pathology or significant collateral ligament insufficiency identified. The mean follow-up was 11 months, with a range of 6 to 42 months. Mean follow-up motion ranged from 2° (range, ⫺5° to 10°) of elbow extension to 142° (range, 125° to 150°) of flexion. Final forearm rotation measured 80° (range, 45° to 90°), with 78° of pronation (range, 65° to 90°). Only 1 patient lost greater than 10° of motion in any plane when compared with the contralateral side. This individual lost 30° of isolated forearm supination. None of the patients had active or passive joint crepitus. All radial head fractures healed clinically and radiographically. At final evaluation, all patients had relief of pain, no restrictions with activities of daily living, and furthermore, no functional difficulties. Case examples
Case 1. A 29-year-old woman fell on the outstretched hand. Radiographs revealed a Mason type I fracture of the radial head with minimal displacement (Figure 1, A and B). On examination 3 days after injury, she had 20° to 120° of elbow motion, with 45° of supination and 20° of pronation. After aspiration of hemarthrosis and intraarticular lidocaine injection, she had significant crepitus and a minimal increase in forearm rotation. Operative exploration was chosen because of the persistent block in motion and the crepitus. Intraoperatively, a fullthickness cartilage fragment of the posterolateral capitellum (approximately 30% of the capitellar surface) wedged completely in the radial head fracture was found (Figure 1, C). The capitellar fragment was excised, and the defect was debrided of loose edges. The radial head fracture was reduced and stabilized with a Herbert screw (Zimmer, Warsaw, IN) (Figure 1, D and E). An uneventful recovery followed. At 1 year postoperatively, the patient reported no pain or dysfunction and recovered symmetric elbow motion and forearm rotation. Case 2. A 23-year-old man injured his nondominant arm while playing basketball. In the office 3 days after the injury, he had a subtle palpable click with forearm rotation. Radiographs revealed a minimally displaced radial head fracture (Figure 2, A and B). The mechanical findings on examination prompted operative intervention. At surgery, a large capitellar fragment wedged in the radial head fracture was found, limiting reduction (Figure 2, C). The capitellar fragment was excised, and the radial head
717
fracture was stabilized with 2 interfragmentary screws (Figure 2, D and E). The click only resolved once the fragment was removed. At 6 months, the patient had 5° to 140° of motion with no pain and with full rotation and normal grip strength. DISCUSSION Fractures of the radial head are the most common skeletal injury in the adult elbow. Most fractures involve a component of articular impaction in addition to shear. The simplest pattern of displacement involves failure of a margin of the head in depression. In higher-energy trauma, concomitant soft-tissue and bony injuries can include the medial or lateral collateral ligaments of the elbow, the interosseous ligament of the forearm, and the coronoid process of the ulna.1,3,4,8,9 Whereas associated cartilaginous injury to the humeral capitellum is not uncommon, a displaced fragment trapped within the radial head fracture is rare and has only been reported sparingly. The first report of this phenomenon dates back to 1916. At the New York Surgical Society, Hitzrot7 presented a case in which a capitellar fragment was engaged into the fracture line of the radius. The preoperative radiographs did not reveal any injury to the capitellum. In 1931 Milch11 described two patients with radial head fractures and osteochondral capitellum injuries, one of which was found to be united within a comminuted radial head fracture. Interestingly, the diagnosis was made based on the preoperative radiographs. Milch described a “peculiar crescentic shadow projecting downward from the humerus and reaching across toward the head of the radius.” In 1978 Heim and Trub6 reported on a series of 20 patients treated with internal fixation for radial head fractures, 2 of which had cartilage lesions of the capitellum interposed in the fracture of the radius. Thereafter, Newman13 reported a case in which a fragment from the capitellum driven as a wedge into the head of the radius was found. The capitellar fragment was excised, and the radial head fracture was repaired. In 1988 Ward and Nunley17 provided a review of combined radial head and capitellar injuries. Over an 11-year period, they identified 29 cases of operatively treated radial head fractures and 13 cases of operatively treated capitellar fractures. Seven patients had combined injuries, and one of these cases involved an osteochondral lesion interposed in the radial head fracture site. In this case, similar to that reported by Milch,11 the fragment included bone from the anterolateral aspect of the capitellum. Interestingly, the incidence of capitellum injury was approximately 1.7% with all radial head fractures, but with more severe injuries (ie,
718
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J Shoulder Elbow Surg November/December 2006
Figure 1 A and B, Preoperative radiographs (lateral and anteroposterior) depicting radial head fracture and no obvious injury to capitellum. C, Intraoperative photograph showing capitellar defect (inferior and posterior to nerve hook) and capitellar cartilage wedged in displaced radial head fracture. D and E, Postoperative radiographs (lateral and anteroposterior) after radial head fixation.
those fractures requiring operative fixation), the incidence rose to 24%. Finally, in a series of 19 radial head fractures treated with internal fixation, Geel et al5 found capitellar osteocartilaginous loose bodies caught within the radial head in 3 cases. They did not state whether these capitellar lesions were noted preoperatively.
We report 10 cases in which a cartilaginous shear fragment from the capitellum was identified at the time of surgery, interposed and blocking reduction of Mason type I and II radial head fractures. Our cases are similar in that all involved a purely cartilaginous fragment of the capitellum that was not suspected preoperatively with plain radio-
J Shoulder Elbow Surg Volume 15, Number 6
Caputo et al
719
Figure 2 A, Preoperative lateral radiograph showing minimally displaced radial head fracture. B, Intraoperative photograph of sheared capitellum cartilage wedged in irreducible radial head fracture. C, Intraoperative photograph after removal of capitellar cartilage fragment (in forceps) from radial head fracture. D and E, Postoperative radiographs after fixation.
graphs or computed tomography. This is likely because of the lack of subchondral bone in the fragments. It is possible that these interposed fragments could have been recognized by magnetic resonance imaging, but this test was not performed in any of the patients. All 10 patients regained nearly full mobility after removal of the interposed carti-
lage fragment, followed by reduction and internal fixation of the radial head. In retrospect, there are very few data that could have allowed us to predict this finding in the majority our cases. Although 5 patients exhibited mechanical symptoms with forearm rotation, this was initially attributed to fracture displacement in 4.
720
Caputo et al
Only in the Mason type I injury was the source of this crepitus difficult to identify preoperatively. In addition, 5 patients had no palpable crepitus or block to rotation preoperatively. Simple marginal shear failure of a portion of the radial head was involved in all (Figures 1 and 2). Although nonunion of the radial head is rare, persistent interposition of a cartilage fragment could theoretically predispose patients to a nonunion or malunion or lead to mechanical symptoms. One of the authors (A.E.C.) has treated a patient with a symptomatic nonunion of the radial head in which a retained cartilage fragment was found within the nonunion site. The natural history of untreated interposed cartilaginous fragments within the radial head is not known. However, this phenomenon may be responsible, in part, for some of the late symptoms reported after the conservative treatment of nondisplaced and minimally displaced shear fractures of the radial head margin.2,15,16 The precise mechanism of the injury pattern described cannot be discerned from this series. Other authors have suggested that associated lesions of the capitellum and radial head are the result of a particular angle at the time of impact,11 but this has not been reproduced experimentally. It does seem plausible that these lesions could occur as a result of a shear injury to the radial head as it is loaded axially against the capitellum.6,14,17 A transient posterolateral subluxation of the radial head could be postulated. Upon spontaneous reduction of the head, the capitellar cartilage fragment could become trapped within the radius. Notably, however, significant lateral joint instability was not found in any of our cases. In summary, this series identifies 10 cases with an unusual pattern in which a capitellar cartilage fragment was trapped within a shear fracture of the radius, blocking reduction. A high suspicion for this injury pattern is indicated in isolated Mason type I and II fractures with mechanical findings during forearm rotation. However, predictive clinical findings
J Shoulder Elbow Surg November/December 2006
may be absent. During operative treatment of the radial head, we recommend careful inspection of the capitellum and thorough joint debridement to remove any loose cartilaginous fragments. REFERENCES
1. Arner O, Ekengren, K, Von Schreeb T. Fractures of the head and neck of the radius: a clinical and roentgenographic study of 310 cases. Acta Chir Scand 1957;112:115-34. 2. Bakalim G. Fractures of radial head and their treatment. Acta Orthop Scand 1970;41:320-31. 3. Davidson PA, Moseley JB Jr, Tullos HS. Radial head fracture. A potentially complex injury. Clin Orthop Relat Res 1993:224-30. 4. Essex-Lopresti P. Fractures of the radial head with distal radioulnar dislocation, report of two cases. J Bone Joint Surg Br 1951;33:244-7. 5. Geel CW, Palmer AK, Ruedi T, Leutenegger AF. Internal fixation of proximal radial head fractures. J Orthop Trauma 1990;4: 270-4. 6. Heim U, Trub HJ. Experiences with primary osteosynthesis in radial head fractures [in German]. Helv Chir Acta 1978;45: 63-9. 7. Hitzrot JM. Comment on open reduction of the capitellum. Ann Surg 1916;63:487. 8. Hotchkiss RN. Displaced fractures of the radial head: internal fixation or excision. J Am Acad Orthop Surg 1997;5:1-10. 9. Liu SH, Henry MH. Fracture of the radial head with ulnar collateral ligament rupture. J Shoulder Elbow Surg 1995;4:399-402. 10. Mason ML. Some observations on fractures of the head of the radius with a review of one hundred cases. Br J Surg 1954;42: 123-32. 11. Milch H. Unusual fractures of the capitulum humeri and the capitulum radii. J Bone Joint Surg 1931;13:882-6. 12. Muller ME, Allgower M, Schneider R, Willenegger H. Manual for internal fixation. New York: Springer-Verlag; 1995. p. 464-5. 13. Newman JH. Radius fractures and damage to the capitulum humeri [letter]. Injury 1983;14:477. 14. Palmer I. The validity of the rule of alternativity in traumatology. Acta Chir Scand 1961;121:481-5. 15. Poulsen JO, Tophoj K. Fracture of the head and neck of the radius. Follow-up on 61 patients. Acta Orthop Scand 1974;45:66-75. 16. Radin EL, Riseborough EJ. Fractures of the radial head. A review of eighty-eight cases and analysis of the indications for excision of the radial head and non-operative treatment. J Bone Joint Surg Am 1966;48:1055-64. 17. Ward WG, Nunley JA. Concomitant fractures of the capitellum and radial head. J Orthop Trauma 1988;2:110-6.
Ten cases of Mason type I and type II isolated radial head fractures are reported, in which an unexpected cartilaginous fragment of the capitellum trapped within the radial head fracture was identified at the time of surgery. In no case was this injury pattern identified on preoperative imaging, including computed tomography in 2 cases. Five patients did have preoperative mechanical findings with forearm rotation. At surgery, all capitellar fragments were found to originate from the posterolateral capitellum. Excision of the capitellar fragment and internal fixation of the radial head fracture were performed in all cases. No sequelae were identified on short-term follow-up. This series highlights an injury pattern that should be considered in isolated nondisplaced and minimally displaced fractures of the radial head. The natural history of this finding, when treated conservatively, is unknown. (J Shoulder Elbow Surg 2006;15:716-720.)
three different surgeons (A.E.C., M.S.C., and G.J.K.). Relative to the total number of operatively treated radial head fractures during the study period, this represents 2 of 26 over a 2-year period (G.J.K.), 3 of 37 over a 3-year period (M.S.C.), and 5 of 55 over a 3-year period (A.E.C.). None of the patients had concomitant soft-tissue or bony injuries of the elbow or upper extremity. Intraoperatively, in all cases, there was an unexpected shear fracture of the capitellar articular cartilage wedged into the radial head fracture blocking reduction. The mean patient age was 33 years, with a range of 18 to 50 years. A retrospective evaluation of the cases was performed. All original radiographs were evaluated in an effort to determine fracture characteristics of this injury complex. Fractures were categorized by the classification of Mason.10 Operative findings were recorded. Collateral ligament insufficiency was assessed by gross observation and, if necessary, intraoperative fluoroscopic stress examination. A final follow-up assessment of function, pain, and fracture healing was performed to determine clinical outcome.
R adial head fractures are the most common frac-
RESULTS
tures of the elbow and have a variety of associated injuries. One of the less recognized, but intuitively obvious of these, is trauma to the capitellum. For fracture to occur, the radial head must be compressed against the humeral capitellum,14 and concomitant radial head and capitellar fractures have been described.5-7,11-13,17 The purpose of this article is to describe 10 unusual cases of radial head fractures in which a cartilage fragment from the posterolateral capitellum was vertically interposed directly into the radial head fracture. Reduction of the radial head fracture was not possible without removal of this cartilaginous fragment. MATERIALS AND METHODS Ten patients underwent open reduction–internal fixation of seemingly isolated displaced radial head fractures by From the Orthopaedic Associates of Hartford. Reprint requests: Andrew E. Caputo, MD, Orthopaedic Associates of Hartford, 85 Seymour St, Suite 607, Hartford, CT 06106. Copyright © 2006 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/2006/$32.00 doi:10.1016/j.jse.2006.01.007
716
The mechanism of injury in all patients was a fall on the outstretched upper extremity. Of the 10 radial head fractures, 9 were Mason type II and 1 was type I. In 5 cases, the decision to operate was, in part, based on limited or painful forearm rotation accompanied by crepitus. In the minimally displaced (type I) case, radiocapitellar crepitus and rotation loss were present despite an intraarticular injection of lidocaine. In the other 5 cases, the decision to proceed with operative fixation was based on the displacement of the radial head fracture and the age and activity level of the patients. Preoperative radiographs did not delineate the capitellar injury in any case. Two patients had preoperative computed tomography scans with 3-dimensional reconstruction. These studies also did not reveal an injury to the capitellum. All patients underwent open reduction–internal fixation of the radial head fragment. At the time of operation, all cases had an unexpected fragment of articular cartilage interposed vertically within the fracture site. Further inspection revealed an articular cartilage defect on the posterolateral aspect of the capitellum. All of the capitellar fragments were relatively small, ranging from 3 ⫻ 5 mm to 10 ⫻ 10 mm. None
Caputo et al
J Shoulder Elbow Surg Volume 15, Number 6
of the capitellar fragments was considered large enough to support stable internal fixation, and therefore, they were excised in all cases. The only treatment for the defect in the capitellum was debridement of loose edges, and specifically, no microfracture techniques were used. In no case was associated intraarticular pathology or significant collateral ligament insufficiency identified. The mean follow-up was 11 months, with a range of 6 to 42 months. Mean follow-up motion ranged from 2° (range, ⫺5° to 10°) of elbow extension to 142° (range, 125° to 150°) of flexion. Final forearm rotation measured 80° (range, 45° to 90°), with 78° of pronation (range, 65° to 90°). Only 1 patient lost greater than 10° of motion in any plane when compared with the contralateral side. This individual lost 30° of isolated forearm supination. None of the patients had active or passive joint crepitus. All radial head fractures healed clinically and radiographically. At final evaluation, all patients had relief of pain, no restrictions with activities of daily living, and furthermore, no functional difficulties. Case examples
Case 1. A 29-year-old woman fell on the outstretched hand. Radiographs revealed a Mason type I fracture of the radial head with minimal displacement (Figure 1, A and B). On examination 3 days after injury, she had 20° to 120° of elbow motion, with 45° of supination and 20° of pronation. After aspiration of hemarthrosis and intraarticular lidocaine injection, she had significant crepitus and a minimal increase in forearm rotation. Operative exploration was chosen because of the persistent block in motion and the crepitus. Intraoperatively, a fullthickness cartilage fragment of the posterolateral capitellum (approximately 30% of the capitellar surface) wedged completely in the radial head fracture was found (Figure 1, C). The capitellar fragment was excised, and the defect was debrided of loose edges. The radial head fracture was reduced and stabilized with a Herbert screw (Zimmer, Warsaw, IN) (Figure 1, D and E). An uneventful recovery followed. At 1 year postoperatively, the patient reported no pain or dysfunction and recovered symmetric elbow motion and forearm rotation. Case 2. A 23-year-old man injured his nondominant arm while playing basketball. In the office 3 days after the injury, he had a subtle palpable click with forearm rotation. Radiographs revealed a minimally displaced radial head fracture (Figure 2, A and B). The mechanical findings on examination prompted operative intervention. At surgery, a large capitellar fragment wedged in the radial head fracture was found, limiting reduction (Figure 2, C). The capitellar fragment was excised, and the radial head
717
fracture was stabilized with 2 interfragmentary screws (Figure 2, D and E). The click only resolved once the fragment was removed. At 6 months, the patient had 5° to 140° of motion with no pain and with full rotation and normal grip strength. DISCUSSION Fractures of the radial head are the most common skeletal injury in the adult elbow. Most fractures involve a component of articular impaction in addition to shear. The simplest pattern of displacement involves failure of a margin of the head in depression. In higher-energy trauma, concomitant soft-tissue and bony injuries can include the medial or lateral collateral ligaments of the elbow, the interosseous ligament of the forearm, and the coronoid process of the ulna.1,3,4,8,9 Whereas associated cartilaginous injury to the humeral capitellum is not uncommon, a displaced fragment trapped within the radial head fracture is rare and has only been reported sparingly. The first report of this phenomenon dates back to 1916. At the New York Surgical Society, Hitzrot7 presented a case in which a capitellar fragment was engaged into the fracture line of the radius. The preoperative radiographs did not reveal any injury to the capitellum. In 1931 Milch11 described two patients with radial head fractures and osteochondral capitellum injuries, one of which was found to be united within a comminuted radial head fracture. Interestingly, the diagnosis was made based on the preoperative radiographs. Milch described a “peculiar crescentic shadow projecting downward from the humerus and reaching across toward the head of the radius.” In 1978 Heim and Trub6 reported on a series of 20 patients treated with internal fixation for radial head fractures, 2 of which had cartilage lesions of the capitellum interposed in the fracture of the radius. Thereafter, Newman13 reported a case in which a fragment from the capitellum driven as a wedge into the head of the radius was found. The capitellar fragment was excised, and the radial head fracture was repaired. In 1988 Ward and Nunley17 provided a review of combined radial head and capitellar injuries. Over an 11-year period, they identified 29 cases of operatively treated radial head fractures and 13 cases of operatively treated capitellar fractures. Seven patients had combined injuries, and one of these cases involved an osteochondral lesion interposed in the radial head fracture site. In this case, similar to that reported by Milch,11 the fragment included bone from the anterolateral aspect of the capitellum. Interestingly, the incidence of capitellum injury was approximately 1.7% with all radial head fractures, but with more severe injuries (ie,
718
Caputo et al
J Shoulder Elbow Surg November/December 2006
Figure 1 A and B, Preoperative radiographs (lateral and anteroposterior) depicting radial head fracture and no obvious injury to capitellum. C, Intraoperative photograph showing capitellar defect (inferior and posterior to nerve hook) and capitellar cartilage wedged in displaced radial head fracture. D and E, Postoperative radiographs (lateral and anteroposterior) after radial head fixation.
those fractures requiring operative fixation), the incidence rose to 24%. Finally, in a series of 19 radial head fractures treated with internal fixation, Geel et al5 found capitellar osteocartilaginous loose bodies caught within the radial head in 3 cases. They did not state whether these capitellar lesions were noted preoperatively.
We report 10 cases in which a cartilaginous shear fragment from the capitellum was identified at the time of surgery, interposed and blocking reduction of Mason type I and II radial head fractures. Our cases are similar in that all involved a purely cartilaginous fragment of the capitellum that was not suspected preoperatively with plain radio-
J Shoulder Elbow Surg Volume 15, Number 6
Caputo et al
719
Figure 2 A, Preoperative lateral radiograph showing minimally displaced radial head fracture. B, Intraoperative photograph of sheared capitellum cartilage wedged in irreducible radial head fracture. C, Intraoperative photograph after removal of capitellar cartilage fragment (in forceps) from radial head fracture. D and E, Postoperative radiographs after fixation.
graphs or computed tomography. This is likely because of the lack of subchondral bone in the fragments. It is possible that these interposed fragments could have been recognized by magnetic resonance imaging, but this test was not performed in any of the patients. All 10 patients regained nearly full mobility after removal of the interposed carti-
lage fragment, followed by reduction and internal fixation of the radial head. In retrospect, there are very few data that could have allowed us to predict this finding in the majority our cases. Although 5 patients exhibited mechanical symptoms with forearm rotation, this was initially attributed to fracture displacement in 4.
720
Caputo et al
Only in the Mason type I injury was the source of this crepitus difficult to identify preoperatively. In addition, 5 patients had no palpable crepitus or block to rotation preoperatively. Simple marginal shear failure of a portion of the radial head was involved in all (Figures 1 and 2). Although nonunion of the radial head is rare, persistent interposition of a cartilage fragment could theoretically predispose patients to a nonunion or malunion or lead to mechanical symptoms. One of the authors (A.E.C.) has treated a patient with a symptomatic nonunion of the radial head in which a retained cartilage fragment was found within the nonunion site. The natural history of untreated interposed cartilaginous fragments within the radial head is not known. However, this phenomenon may be responsible, in part, for some of the late symptoms reported after the conservative treatment of nondisplaced and minimally displaced shear fractures of the radial head margin.2,15,16 The precise mechanism of the injury pattern described cannot be discerned from this series. Other authors have suggested that associated lesions of the capitellum and radial head are the result of a particular angle at the time of impact,11 but this has not been reproduced experimentally. It does seem plausible that these lesions could occur as a result of a shear injury to the radial head as it is loaded axially against the capitellum.6,14,17 A transient posterolateral subluxation of the radial head could be postulated. Upon spontaneous reduction of the head, the capitellar cartilage fragment could become trapped within the radius. Notably, however, significant lateral joint instability was not found in any of our cases. In summary, this series identifies 10 cases with an unusual pattern in which a capitellar cartilage fragment was trapped within a shear fracture of the radius, blocking reduction. A high suspicion for this injury pattern is indicated in isolated Mason type I and II fractures with mechanical findings during forearm rotation. However, predictive clinical findings
J Shoulder Elbow Surg November/December 2006
may be absent. During operative treatment of the radial head, we recommend careful inspection of the capitellum and thorough joint debridement to remove any loose cartilaginous fragments. REFERENCES
1. Arner O, Ekengren, K, Von Schreeb T. Fractures of the head and neck of the radius: a clinical and roentgenographic study of 310 cases. Acta Chir Scand 1957;112:115-34. 2. Bakalim G. Fractures of radial head and their treatment. Acta Orthop Scand 1970;41:320-31. 3. Davidson PA, Moseley JB Jr, Tullos HS. Radial head fracture. A potentially complex injury. Clin Orthop Relat Res 1993:224-30. 4. Essex-Lopresti P. Fractures of the radial head with distal radioulnar dislocation, report of two cases. J Bone Joint Surg Br 1951;33:244-7. 5. Geel CW, Palmer AK, Ruedi T, Leutenegger AF. Internal fixation of proximal radial head fractures. J Orthop Trauma 1990;4: 270-4. 6. Heim U, Trub HJ. Experiences with primary osteosynthesis in radial head fractures [in German]. Helv Chir Acta 1978;45: 63-9. 7. Hitzrot JM. Comment on open reduction of the capitellum. Ann Surg 1916;63:487. 8. Hotchkiss RN. Displaced fractures of the radial head: internal fixation or excision. J Am Acad Orthop Surg 1997;5:1-10. 9. Liu SH, Henry MH. Fracture of the radial head with ulnar collateral ligament rupture. J Shoulder Elbow Surg 1995;4:399-402. 10. Mason ML. Some observations on fractures of the head of the radius with a review of one hundred cases. Br J Surg 1954;42: 123-32. 11. Milch H. Unusual fractures of the capitulum humeri and the capitulum radii. J Bone Joint Surg 1931;13:882-6. 12. Muller ME, Allgower M, Schneider R, Willenegger H. Manual for internal fixation. New York: Springer-Verlag; 1995. p. 464-5. 13. Newman JH. Radius fractures and damage to the capitulum humeri [letter]. Injury 1983;14:477. 14. Palmer I. The validity of the rule of alternativity in traumatology. Acta Chir Scand 1961;121:481-5. 15. Poulsen JO, Tophoj K. Fracture of the head and neck of the radius. Follow-up on 61 patients. Acta Orthop Scand 1974;45:66-75. 16. Radin EL, Riseborough EJ. Fractures of the radial head. A review of eighty-eight cases and analysis of the indications for excision of the radial head and non-operative treatment. J Bone Joint Surg Am 1966;48:1055-64. 17. Ward WG, Nunley JA. Concomitant fractures of the capitellum and radial head. J Orthop Trauma 1988;2:110-6.