- Email: [email protected]
Loss of flexion after radial head replacement
Loss of flexion after radial head replacement John P. Birkedal, MD, D. Nicole Deal, MD, and David S. Ruch, MD, Winston-Salem, NC
Prosthetic radial head replacement is a well-documented procedure; however, loss of elbow flexion after radial head arthroplasty has only recently been reported. This study reviews 6 patients who received modular prosthetic radial heads and had a clinically significant decrease in elbow flexion. The implant was removed in 4 of these patients because of reduced elbow motion and pain. This clinical finding is correlated with biomechanical data obtained by use of matched-pair, fresh-frozen upper extremity specimens loaded to 330 N with the forearm in positions of neutral, pronation, and supination for each of three elbow positions (0°, 90°, and 135°). The radiocapitellar gap was monitored and was significantly smaller under load during elbow flexion compared with extension. This study indicates the need for verification of the radiocapitellar gap throughout elbow range of motion in order to prevent these complications. (J Shoulder Elbow Surg 2004;13:208-13.)
T
he frequency of radial head and neck fracture has been reported to be between 1.7% to 5.4% of all fractures and accounts for 33% of elbow fractures.14 Eighty-five percent of fractures occur in persons between 20 and 60 years of age, with a mean age between 30 and 40 years.14 The mechanism of injury of most radial head fractures is a fall on the outstretched hand with the elbow partially flexed and pronated.14 The most common treatments for radial head fractures include open reduction and internal fixation and radial head resection with or without prosthetic radial head replacement. There is no consensus regarding the best treatment for Mason type III fractures with severe comminution of the radial head; however, most authors agree that salvage and internal fixation of the radial head are preferred.7 Radial From the Department of Orthopaedic Surgery, Wake Forest University. Supported by a National Institutes of Health Physician Scientist Training Grant (No. T32 HL 07868). Reprint requests: David S. Ruch, MD, Department of Orthopaedic Surgery, Wake Forest University, 4th Floor Watlington Hall, Medical Center Blvd, Winston-Salem, NC 27157 (E-mail: [email protected]). Copyright © 2004 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/2004/$35.00 ⫹ 0 doi:10.1016/j.jse.2003.11.007
208
head resection is generally recommended only for displaced, comminuted fractures that involve greater than 50% of the head14 and cannot be repaired by stable internal fixation. When stable internal fixation is not possible and forearm and/or elbow instability is present, radial head resection with prosthetic replacement is an option. The principal goals of treatment are to maintain the longitudinal radioulnar relationship8 and to preserve elbow motion and stability. The structures critical for postresection stability include the posterolateral ligament complex at the elbow, the anterior bundle of the medial collateral ligament, the interosseous membrane (IOM) of the forearm, the triangular fibrocartilage complex (TFCC) at the distal radioulnar joint, and an intact coronoid.8,15 Studies have shown that the radial head can be resected after injury without significant proximal radial migration as long as the associated soft-tissue constraints (IOM and TFCC) remain intact.3,4 Hotchkiss et al6 reported that the central portion of the IOM contributes 71% and the TFCC contributes 8% to the mechanical stiffness of the forearm. After injury to these stabilizing structures, complications such as proximal migration of the radius with impingement and eburnation of the capitellum, elbow instability, and ulnar wrist pain with blocking of supination6 can occur. Prosthetic radial head replacement has been advocated in an effort to prevent these complications and improve elbow stability after radial head resection.9 This study retrospectively reviews 6 patients after prosthetic radial head replacement who were found to have a clinically significant decrease in elbow flexion after this procedure requiring removal of the prosthesis in 4 patients. This clinical finding is correlated with biomechanical cadaveric data demonstrating a decreased radiocapitellar gap under load in flexion compared with extension. The study hypothesis is that the clinical loss of flexion after prosthetic radial head placement is a result of a decrease in radiocapitellar gap under load in flexion as compared with extension. MATERIALS AND METHODS Clinical From 1997 to 2001, 22 radial head replacements were performed in 22 patients (16 men and 4 women). The indications for radial head arthroplasty in this patient pop-
J Shoulder Elbow Surg Volume 13, Number 2
ulation were an unreconstructable radial head that consisted of 4 or more fragments of the articular surface and one of the following coexisting factors: (1) persistent humeral-ulnar instability despite osteosynthesis of the olecranon (n ⫽ 12), (2) persistent posterolateral instability after radial head fracture and resection (n ⫽ 6), and (3) longitudinal instability of the forearm resulting from coexistent interosseous ligament and triangular fibrocartilage ligament injury (n ⫽ 4). Sixteen patients were followed up clinically for a mean of 1.5 years. Physical examination was performed with a goniometer by a certified occupational therapist. The mean loss of extension in these patients was 28° (range, 22°-48°). The mean loss of elbow flexion was 15° (range, 6°-60°). All patients had the rotational arc of motion restored to within 10° of the contralateral side. Of the 16 patients, 6 complained chiefly of loss of elbow flexion after radial head replacement. The arc of motion was measured and compared with the contralateral side. The mean arc of motion of these 6 patients was only 79°, with the loss of flexion averaging 49°. The indication for the original radial head replacement in these patients was instability after osteosynthesis of the olecranon in complex fracture dislocations. All patients had had high-energy injuries resulting in comminuted fractures of the olecranon with associated unreconstructable radial head fracture dislocations. All patients were treated with osteosynthesis of the olecranon by use of 3.5-mm reconstruction plates and had associated repair of the coronoid fracture. All cases were noted to have persistent instability after stabilization of the olecranon as a result of failure of the lateral ligamentous complex to stabilize the residual proximal radius adequately after radial head resection. A modular designed radial head (Wright Medical, Arlington, TN) was sized and implanted. The radial head was replaced via the posterior approach while plating the olecranon in all 6 cases. Attention was paid to repairing the lateral ulnar collateral ligament to bone when possible. Protected range of motion was initiated at 3 to 5 days postoperatively in all cases. This consisted of active assisted range of motion from 90° to as much flexion as could be obtained. By 1.5 weeks postoperatively (range, 3-20 days), full range of motion was permitted in all patients.
Biomechanical Six pairs of fresh-frozen cadaveric upper limbs were examined by fluoroscopy to eliminate any specimens with bony pathology from testing. After testing, the IOM was explored and data from any specimen with disruption of the central band were excluded. An experimental testing apparatus was designed to support the cadaveric arm with the elbow at positions of 0° to 135° of flexion (Figure 1). The humerus was fully constrained and the forearm only partially constrained, allowing controlled pronation and supination. By use of a pulley system capable of transmitting forces up to 350 N, an incremental axial force was applied through an external fixator attached to the radius. The support mechanism and load apparatus were capable of flexing and telescoping to achieve a position that permitted longitudinal loading of the radius. A load cell was used to verify the load applied. Linear variable differential transformers (LVDTs), one on the radius and one on the humerus, recorded longitudinal displacement of the radius with re-
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Figure 1 Biomechanical testing apparatus.
spect to the fixed humerus. Before loading, the baseline measurement on the LVDTs was recorded, and then the final measurement was subtracted from the initial measurement, allowing displacement to be determined. The humeral LVDT was placed only to ensure that the position of the humerus did not change, thus ensuring that the change in the radiocapitellar gap was based only on motion of the radius. The load cell and LVDTs were calibrated with a strain gauge before each experimental cycle. Specimens were prepared by transverse osteotomy 25 cm proximal to the elbow joint. Soft tissues were removed from the humerus 5 cm proximal to the elbow joint, which allowed placement of the denuded humerus on a split resin mold to secure the arm in the testing apparatus. Three half-pins were then inserted at 5-cm increments, starting with the first pin 2 cm proximal to the radiocarpal articulation, ensuring that the pins passed through both cortices of the radius. These pins were attached to the external fixator and transmitted the load to the radius. Two additional half-pins were placed, one in the proximal radius 1.5 cm from the radiocapitellar joint and one in the lateral distal humerus. The additional radial pin was used to measure radial displacement, and the additional humeral pin was used to measure minimal displacements of the humerus with
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Figure 2 Range of motion with prosthetic radial head implant (top). Increased range of motion after prosthetic radial head implant removal (bottom)
loading. The specimens were then placed in the testing apparatus, and baseline measurements with 90° elbow flexion were obtained in neutral, 60° supination, and 60° pronation positions. Seven millimeters of radial head was resected from each specimen. Axial forces were applied incrementally to a final load of 330 N, a load chosen to simulate the activities of daily living at one-half body weight.12 The applied load was measured by use of the load cell, and displacement was measured by use of two LVDTs. Lateral fluoroscopic images of the elbow were obtained before and after loading in each forearm position to radiographically document the radiocapitellar gap. The radiocapitellar gap was measured with respect to a known reference (a 5-mm arthroscopic right angle placed inside the joint) on these radiographic images and, along with the displacement data from the LVDTs, was used to determine the radiocapitellar gap under load. Measurements were taken for three load cycles at each elbow and forearm position. Radiocapitellar gap data were converted mathematically to percent gap by dividing the measured gap under load by the measured initial gap before the start of the load cycle. Stiffness (in Newtons of force per millimeter of displacement) of the soft-tissue constraints was determined by graphical tech-
niques with the use of a best-fit curve through the forcedisplacement profile of the three load cycles.
Statistical Repeated-measures analysis of variance was used to detect differences in radial displacement under load resulting from forearm position (neutral, supination, and pronation) and degree of elbow flexion (0°, 90°, and 135°). A compound symmetry covariance structure was used to model observations. Models examined included all main effects plus all 2-way interactions. The best predictors of radiocapitellar gap were determined by use of backward stepwise elimination. The final model chosen contained only those terms significant at the P ⬍ .05 level.
RESULTS Clinical
The implant was removed in 4 patients (Figure 2). These 4 patients had a mean increase in total elbow range of motion of 39°, with a mean increase in elbow flexion of 26° after prosthesis removal (Table
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Table I Increases in ROM and flexion after prosthesis removal
Patient Patient Patient Patient
1 2 3 4
ROM with radial head prosthesis
ROM after removal of prosthesis
Increase in ROM after removal
Increase in flexion after removal
50°–105° 55°–120° 50°–110° 45°–65°
45°–125° 35°–125° 40°–130° 30°–125°
25° 25° 30° 75°
20° 5° 20° 60°
DISCUSSION
Figure 3 Percent gap at 330 N versus degree of elbow flexion: Graph demonstrating a significantly larger percentage of radiocapitellar gap in full extension (0°) as compared with full flexion (135°) (P ⬍ .04).
I). They also were noted to have complete eburnation with trough erosion of the anterior capitellum without significant erosion of the distal capitellum. Biomechanical
Biomechanical data demonstrated a significantly smaller radiocapitellar gap in full flexion (135°) than in full extension (0°) with a load of 330 N (P ⬍ .04) regardless of forearm position (neutral, supination, or pronation) (Figure 3). The radiocapitellar gap varied slightly under load between forearm positions but showed no significant difference (neutral, 35.0%; supination, 45.5%; and pronation, 36.6%) (P ⫽ .47). The stiffness of the soft-tissue constraints averaged 86.9 N/mm with variation between forearm positions but was not statistically significant (neutral, 78.0 N/mm; supination, 84.4 N/mm; and pronation, 97.8 N/mm).
Patients often have decreased elbow range of motion after major surgery; however, the preferential loss of elbow flexion after a radial head resection with replacement is not expected. In this clinical study 6 patients who had modular prosthetic radial heads placed were evaluated because of loss of motion and pain. Four of these patients had their implants removed as a result of these complications. This study correlates the clinical finding of decreased flexion after prosthetic radial head replacement with biomechanical data demonstrating a decreased radiocapitellar gap under load with the elbow in full flexion compared with full extension regardless of forearm position. Moro et al11 also reported a loss of elbow flexion after arthroplasty with metal prostheses for unreconstructable radial head fractures. In a retrospective review of 25 displaced unreconstructable fractures, a significant loss of elbow flexion was noted in the affected extremity when compared with the unaffected extremity at follow-up (mean, 39 months). Moro et al also noted changes in load transfer after prosthetic radial head placement, which supports the clinical observation in this study of capitellar eburnation after arthroplasty. Among authors advocating prosthetic radial head replacement, the type of prosthesis (silicone vs titanium) also has been a subject of debate.9 However, recent studies have reported good long-term results in patients with metallic radial head implants.5 All patients in the present study were fitted with modular metal prostheses. In a clinical study of 36 comminuted radial head fractures treated with primary replacement, the implant was noted to provide stability that allowed soft-tissue healing.10 However, each of the 4 patients who had their prosthesis removed because of loss of flexion and pain demonstrated improved stability and range of motion after removal of the prosthesis. Many studies have modeled sequential injury to the IOM, central band, and TFCC,2,6,17,18 demonstrating that the most significant restraint to proximal migration appears to be the central band of the IOM.6 Radial displacement and load transfer would be altered with partial or complete disruption of the
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Figure 4 Modular trial implant prosthesis with a 4-mm augmented neck length. The prosthesis is firmly in contact with the capitellum in extension (left) and is tightly opposed to the anterior surface of the capitellum in flexion (right).
Figure 5 Standard neck-length prosthesis without a 4-mm augmentation. The prosthesis does not make contact with the capitellum in extension (left) and only makes firm contact with the anterior surface of the capitellum in flexion (right).
IOM. In this biomechanical study the mean soft-tissue stiffness of 86.9 N/mm correlates with previous studies,6,16 all IOMs were intact, and no attempt was made to model this difference. Other studies also have noted decreased radiocapitellar gap with forearm pronation compared with other forearm positions.13 However, a potential limitation of the present analysis is that it only describes the effect of an external load transmitted through the radius and does not model internal muscle reaction forces as other studies have.9 Anatomic studies1 have shown that elbow flexion is limited by the impact of the radial head against the radial fossa, the impact of the coronoid process against the coronoid fossa, and the tension of the joint capsule and triceps. However, there are many com-
plex soft-tissue constraints at the elbow that provide stability for the radiocapitellar articulation. The biomechanical data from this study suggest a possible cause for increased capitellar wear but do not exclusively describe the phenomenon. Further study is warranted to determine the most significant anatomic factor contributing to this change in compliance and decreased radiocapitellar gap under load with elbow flexion. In addition, anatomic factors that could contribute to anterior capitellar wear and decreased flexion must be further elucidated. The greatest decrease in radiocapitellar gap under load occurs in full elbow flexion, whereas in extension, the radiocapitellar gap remains the largest. Measurement of the radiocapitellar gap in extension may lead to overstuffing and predispose to decreased
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radiocapitellar gap during elbow flexion after prosthetic radial head placement (Figures 4 and 5). The clinical and biomechanical data presented in this study indicate that overstuffing of the prosthesis in the radiocapitellar joint is a potential pitfall in the technique of radial head arthroplasty. The implant is routinely placed with the elbow in extension to facilitate broaching and stem placement. Although this position serves to prevent associated injury to the adjacent articular surfaces, it makes it critical to assess the fit of the prosthesis as the elbow is brought into full flexion. In addition, care must be taken to avoid eccentric broaching of the prostheses so as not to direct the prosthesis posterolaterally. Whereas there is the need for attention to detail in addressing the fit of the prosthesis in elbow flexion, there is also the issue of improved stability afforded in elbow extension. As with any arthroplasty technique, there is a balance between the enhanced stability seen with radial head arthroplasty versus the potential loss of motion, and an appropriate balance must be achieved. We thank Julia T. Rushing, MSTAT, for assistance with statistical analysis and E. Stanley Gordon, BS, for technical assistance with biomechanical testing. REFERENCES
1. An KN, Morrey BF. Biomechanics of the elbow. In: Morrey BF, editor. The elbow and its disorders. 2nd ed. Philadelphia: Saunders; 1993. p. 383-404. 2. Birkbeck DP, Faill JM, Hoshaw SJ, Fyhrie DP, Schaffler M. The interosseous membrane affects load distribution in the forearm. J Hand Surg [Am] 1997;22:975-80. 3. Coleman DA, Blair WF, Shurr D. Resection of the radial head for fracture of the radial head. J Bone Joint Surg Am 1987;69:38592.
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4. Fuchs S, Chylarecki C. Do functional deficits result from radial head resection? J Shoulder Elbow Surg 1999;8:247-51. 5. Harrington IJ, Sekyi-Otu A, Barrington TW, Evans DC, Tuli V. The functional outcome with metallic radial head implants in the treatment of unstable elbow fractures: a long-term review. J Trauma 2001;50:46-52. 6. Hotchkiss RN, An KN, Sowa DT, Basta S, Weiland AJ. An anatomic and mechanical study of the interosseous membrane of the forearm: pathomechanics of proximal migration of the radius. J Hand Surg [Am] 1989;14:256-61. 7. Hotchkiss RN. Displaced fractures of the radial head: internal fixation or excision? J Am Acad Orthop Surg 1997;5:1-10. 8. Hotchkiss RN. Fractures of the radial head and related instability and contracture of the forearm. Instr Course Lect 1998;47: 173-7. 9. King GJW, Zarzour ZDS, Rath DA, et al. Metallic radial head arthroplasty improves valgus stability of the elbow. Clin Orthop 1999;368:114-25. 10. Knight DJ, Rymaszewski LA, Amis AA, Miller JH. Primary replacement of the fractured radial head with a metal prosthesis. J Bone Joint Surg Br 1993;75:572-6. 11. Moro JK, Werier J, MacDermid JC, Patterson SD, King GJW. Arthroplasty with a metal radial head for unreconstructible fractures of the radial head. J Bone Joint Surg Am 2001;83:120211. 12. Morrey BF. Applied anatomy and biomechanics of the elbow joint. Instr Course Lect 1986;35:59-68. 13. Morrey BF, An KN, Stormont TJ. Force transmission through the radial head. J Bone Joint Surg Am 1988;70:250-6. 14. Morrey BF. Radial head fracture. In: Morrey BF, editor. The elbow and its disorders. 2nd ed. Philadelphia: Saunders; 1993. p. 383-404. 15. Rabinowitz RS, Light TR, Havey RM, et al. The role of the interosseous membrane and triangular fibrocartilage complex in forearm stability. J Hand Surg [Am] 1994;19:385-93. 16. Sellman DC, Seitz WH Jr, Postak PD, Greenwald AS. Reconstructive strategies for radio-ulnar dissociation: a biomechanical study. J Orthop Trauma 1995;9:516-22. 17. Skahen JR III, Palmer AK, Werner FW, Fortino MD. Reconstruction of the interosseous membrane of the forearm in cadavers. J Hand Surg [Am] 1997;22:986-94. 18. Werner FW, An KN. Biomechanics of the elbow and forearm. Hand Clin 1994;10:357-73.
Prosthetic radial head replacement is a well-documented procedure; however, loss of elbow flexion after radial head arthroplasty has only recently been reported. This study reviews 6 patients who received modular prosthetic radial heads and had a clinically significant decrease in elbow flexion. The implant was removed in 4 of these patients because of reduced elbow motion and pain. This clinical finding is correlated with biomechanical data obtained by use of matched-pair, fresh-frozen upper extremity specimens loaded to 330 N with the forearm in positions of neutral, pronation, and supination for each of three elbow positions (0°, 90°, and 135°). The radiocapitellar gap was monitored and was significantly smaller under load during elbow flexion compared with extension. This study indicates the need for verification of the radiocapitellar gap throughout elbow range of motion in order to prevent these complications. (J Shoulder Elbow Surg 2004;13:208-13.)
T
he frequency of radial head and neck fracture has been reported to be between 1.7% to 5.4% of all fractures and accounts for 33% of elbow fractures.14 Eighty-five percent of fractures occur in persons between 20 and 60 years of age, with a mean age between 30 and 40 years.14 The mechanism of injury of most radial head fractures is a fall on the outstretched hand with the elbow partially flexed and pronated.14 The most common treatments for radial head fractures include open reduction and internal fixation and radial head resection with or without prosthetic radial head replacement. There is no consensus regarding the best treatment for Mason type III fractures with severe comminution of the radial head; however, most authors agree that salvage and internal fixation of the radial head are preferred.7 Radial From the Department of Orthopaedic Surgery, Wake Forest University. Supported by a National Institutes of Health Physician Scientist Training Grant (No. T32 HL 07868). Reprint requests: David S. Ruch, MD, Department of Orthopaedic Surgery, Wake Forest University, 4th Floor Watlington Hall, Medical Center Blvd, Winston-Salem, NC 27157 (E-mail: [email protected]). Copyright © 2004 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/2004/$35.00 ⫹ 0 doi:10.1016/j.jse.2003.11.007
208
head resection is generally recommended only for displaced, comminuted fractures that involve greater than 50% of the head14 and cannot be repaired by stable internal fixation. When stable internal fixation is not possible and forearm and/or elbow instability is present, radial head resection with prosthetic replacement is an option. The principal goals of treatment are to maintain the longitudinal radioulnar relationship8 and to preserve elbow motion and stability. The structures critical for postresection stability include the posterolateral ligament complex at the elbow, the anterior bundle of the medial collateral ligament, the interosseous membrane (IOM) of the forearm, the triangular fibrocartilage complex (TFCC) at the distal radioulnar joint, and an intact coronoid.8,15 Studies have shown that the radial head can be resected after injury without significant proximal radial migration as long as the associated soft-tissue constraints (IOM and TFCC) remain intact.3,4 Hotchkiss et al6 reported that the central portion of the IOM contributes 71% and the TFCC contributes 8% to the mechanical stiffness of the forearm. After injury to these stabilizing structures, complications such as proximal migration of the radius with impingement and eburnation of the capitellum, elbow instability, and ulnar wrist pain with blocking of supination6 can occur. Prosthetic radial head replacement has been advocated in an effort to prevent these complications and improve elbow stability after radial head resection.9 This study retrospectively reviews 6 patients after prosthetic radial head replacement who were found to have a clinically significant decrease in elbow flexion after this procedure requiring removal of the prosthesis in 4 patients. This clinical finding is correlated with biomechanical cadaveric data demonstrating a decreased radiocapitellar gap under load in flexion compared with extension. The study hypothesis is that the clinical loss of flexion after prosthetic radial head placement is a result of a decrease in radiocapitellar gap under load in flexion as compared with extension. MATERIALS AND METHODS Clinical From 1997 to 2001, 22 radial head replacements were performed in 22 patients (16 men and 4 women). The indications for radial head arthroplasty in this patient pop-
J Shoulder Elbow Surg Volume 13, Number 2
ulation were an unreconstructable radial head that consisted of 4 or more fragments of the articular surface and one of the following coexisting factors: (1) persistent humeral-ulnar instability despite osteosynthesis of the olecranon (n ⫽ 12), (2) persistent posterolateral instability after radial head fracture and resection (n ⫽ 6), and (3) longitudinal instability of the forearm resulting from coexistent interosseous ligament and triangular fibrocartilage ligament injury (n ⫽ 4). Sixteen patients were followed up clinically for a mean of 1.5 years. Physical examination was performed with a goniometer by a certified occupational therapist. The mean loss of extension in these patients was 28° (range, 22°-48°). The mean loss of elbow flexion was 15° (range, 6°-60°). All patients had the rotational arc of motion restored to within 10° of the contralateral side. Of the 16 patients, 6 complained chiefly of loss of elbow flexion after radial head replacement. The arc of motion was measured and compared with the contralateral side. The mean arc of motion of these 6 patients was only 79°, with the loss of flexion averaging 49°. The indication for the original radial head replacement in these patients was instability after osteosynthesis of the olecranon in complex fracture dislocations. All patients had had high-energy injuries resulting in comminuted fractures of the olecranon with associated unreconstructable radial head fracture dislocations. All patients were treated with osteosynthesis of the olecranon by use of 3.5-mm reconstruction plates and had associated repair of the coronoid fracture. All cases were noted to have persistent instability after stabilization of the olecranon as a result of failure of the lateral ligamentous complex to stabilize the residual proximal radius adequately after radial head resection. A modular designed radial head (Wright Medical, Arlington, TN) was sized and implanted. The radial head was replaced via the posterior approach while plating the olecranon in all 6 cases. Attention was paid to repairing the lateral ulnar collateral ligament to bone when possible. Protected range of motion was initiated at 3 to 5 days postoperatively in all cases. This consisted of active assisted range of motion from 90° to as much flexion as could be obtained. By 1.5 weeks postoperatively (range, 3-20 days), full range of motion was permitted in all patients.
Biomechanical Six pairs of fresh-frozen cadaveric upper limbs were examined by fluoroscopy to eliminate any specimens with bony pathology from testing. After testing, the IOM was explored and data from any specimen with disruption of the central band were excluded. An experimental testing apparatus was designed to support the cadaveric arm with the elbow at positions of 0° to 135° of flexion (Figure 1). The humerus was fully constrained and the forearm only partially constrained, allowing controlled pronation and supination. By use of a pulley system capable of transmitting forces up to 350 N, an incremental axial force was applied through an external fixator attached to the radius. The support mechanism and load apparatus were capable of flexing and telescoping to achieve a position that permitted longitudinal loading of the radius. A load cell was used to verify the load applied. Linear variable differential transformers (LVDTs), one on the radius and one on the humerus, recorded longitudinal displacement of the radius with re-
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Figure 1 Biomechanical testing apparatus.
spect to the fixed humerus. Before loading, the baseline measurement on the LVDTs was recorded, and then the final measurement was subtracted from the initial measurement, allowing displacement to be determined. The humeral LVDT was placed only to ensure that the position of the humerus did not change, thus ensuring that the change in the radiocapitellar gap was based only on motion of the radius. The load cell and LVDTs were calibrated with a strain gauge before each experimental cycle. Specimens were prepared by transverse osteotomy 25 cm proximal to the elbow joint. Soft tissues were removed from the humerus 5 cm proximal to the elbow joint, which allowed placement of the denuded humerus on a split resin mold to secure the arm in the testing apparatus. Three half-pins were then inserted at 5-cm increments, starting with the first pin 2 cm proximal to the radiocarpal articulation, ensuring that the pins passed through both cortices of the radius. These pins were attached to the external fixator and transmitted the load to the radius. Two additional half-pins were placed, one in the proximal radius 1.5 cm from the radiocapitellar joint and one in the lateral distal humerus. The additional radial pin was used to measure radial displacement, and the additional humeral pin was used to measure minimal displacements of the humerus with
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Figure 2 Range of motion with prosthetic radial head implant (top). Increased range of motion after prosthetic radial head implant removal (bottom)
loading. The specimens were then placed in the testing apparatus, and baseline measurements with 90° elbow flexion were obtained in neutral, 60° supination, and 60° pronation positions. Seven millimeters of radial head was resected from each specimen. Axial forces were applied incrementally to a final load of 330 N, a load chosen to simulate the activities of daily living at one-half body weight.12 The applied load was measured by use of the load cell, and displacement was measured by use of two LVDTs. Lateral fluoroscopic images of the elbow were obtained before and after loading in each forearm position to radiographically document the radiocapitellar gap. The radiocapitellar gap was measured with respect to a known reference (a 5-mm arthroscopic right angle placed inside the joint) on these radiographic images and, along with the displacement data from the LVDTs, was used to determine the radiocapitellar gap under load. Measurements were taken for three load cycles at each elbow and forearm position. Radiocapitellar gap data were converted mathematically to percent gap by dividing the measured gap under load by the measured initial gap before the start of the load cycle. Stiffness (in Newtons of force per millimeter of displacement) of the soft-tissue constraints was determined by graphical tech-
niques with the use of a best-fit curve through the forcedisplacement profile of the three load cycles.
Statistical Repeated-measures analysis of variance was used to detect differences in radial displacement under load resulting from forearm position (neutral, supination, and pronation) and degree of elbow flexion (0°, 90°, and 135°). A compound symmetry covariance structure was used to model observations. Models examined included all main effects plus all 2-way interactions. The best predictors of radiocapitellar gap were determined by use of backward stepwise elimination. The final model chosen contained only those terms significant at the P ⬍ .05 level.
RESULTS Clinical
The implant was removed in 4 patients (Figure 2). These 4 patients had a mean increase in total elbow range of motion of 39°, with a mean increase in elbow flexion of 26° after prosthesis removal (Table
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Table I Increases in ROM and flexion after prosthesis removal
Patient Patient Patient Patient
1 2 3 4
ROM with radial head prosthesis
ROM after removal of prosthesis
Increase in ROM after removal
Increase in flexion after removal
50°–105° 55°–120° 50°–110° 45°–65°
45°–125° 35°–125° 40°–130° 30°–125°
25° 25° 30° 75°
20° 5° 20° 60°
DISCUSSION
Figure 3 Percent gap at 330 N versus degree of elbow flexion: Graph demonstrating a significantly larger percentage of radiocapitellar gap in full extension (0°) as compared with full flexion (135°) (P ⬍ .04).
I). They also were noted to have complete eburnation with trough erosion of the anterior capitellum without significant erosion of the distal capitellum. Biomechanical
Biomechanical data demonstrated a significantly smaller radiocapitellar gap in full flexion (135°) than in full extension (0°) with a load of 330 N (P ⬍ .04) regardless of forearm position (neutral, supination, or pronation) (Figure 3). The radiocapitellar gap varied slightly under load between forearm positions but showed no significant difference (neutral, 35.0%; supination, 45.5%; and pronation, 36.6%) (P ⫽ .47). The stiffness of the soft-tissue constraints averaged 86.9 N/mm with variation between forearm positions but was not statistically significant (neutral, 78.0 N/mm; supination, 84.4 N/mm; and pronation, 97.8 N/mm).
Patients often have decreased elbow range of motion after major surgery; however, the preferential loss of elbow flexion after a radial head resection with replacement is not expected. In this clinical study 6 patients who had modular prosthetic radial heads placed were evaluated because of loss of motion and pain. Four of these patients had their implants removed as a result of these complications. This study correlates the clinical finding of decreased flexion after prosthetic radial head replacement with biomechanical data demonstrating a decreased radiocapitellar gap under load with the elbow in full flexion compared with full extension regardless of forearm position. Moro et al11 also reported a loss of elbow flexion after arthroplasty with metal prostheses for unreconstructable radial head fractures. In a retrospective review of 25 displaced unreconstructable fractures, a significant loss of elbow flexion was noted in the affected extremity when compared with the unaffected extremity at follow-up (mean, 39 months). Moro et al also noted changes in load transfer after prosthetic radial head placement, which supports the clinical observation in this study of capitellar eburnation after arthroplasty. Among authors advocating prosthetic radial head replacement, the type of prosthesis (silicone vs titanium) also has been a subject of debate.9 However, recent studies have reported good long-term results in patients with metallic radial head implants.5 All patients in the present study were fitted with modular metal prostheses. In a clinical study of 36 comminuted radial head fractures treated with primary replacement, the implant was noted to provide stability that allowed soft-tissue healing.10 However, each of the 4 patients who had their prosthesis removed because of loss of flexion and pain demonstrated improved stability and range of motion after removal of the prosthesis. Many studies have modeled sequential injury to the IOM, central band, and TFCC,2,6,17,18 demonstrating that the most significant restraint to proximal migration appears to be the central band of the IOM.6 Radial displacement and load transfer would be altered with partial or complete disruption of the
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Figure 4 Modular trial implant prosthesis with a 4-mm augmented neck length. The prosthesis is firmly in contact with the capitellum in extension (left) and is tightly opposed to the anterior surface of the capitellum in flexion (right).
Figure 5 Standard neck-length prosthesis without a 4-mm augmentation. The prosthesis does not make contact with the capitellum in extension (left) and only makes firm contact with the anterior surface of the capitellum in flexion (right).
IOM. In this biomechanical study the mean soft-tissue stiffness of 86.9 N/mm correlates with previous studies,6,16 all IOMs were intact, and no attempt was made to model this difference. Other studies also have noted decreased radiocapitellar gap with forearm pronation compared with other forearm positions.13 However, a potential limitation of the present analysis is that it only describes the effect of an external load transmitted through the radius and does not model internal muscle reaction forces as other studies have.9 Anatomic studies1 have shown that elbow flexion is limited by the impact of the radial head against the radial fossa, the impact of the coronoid process against the coronoid fossa, and the tension of the joint capsule and triceps. However, there are many com-
plex soft-tissue constraints at the elbow that provide stability for the radiocapitellar articulation. The biomechanical data from this study suggest a possible cause for increased capitellar wear but do not exclusively describe the phenomenon. Further study is warranted to determine the most significant anatomic factor contributing to this change in compliance and decreased radiocapitellar gap under load with elbow flexion. In addition, anatomic factors that could contribute to anterior capitellar wear and decreased flexion must be further elucidated. The greatest decrease in radiocapitellar gap under load occurs in full elbow flexion, whereas in extension, the radiocapitellar gap remains the largest. Measurement of the radiocapitellar gap in extension may lead to overstuffing and predispose to decreased
J Shoulder Elbow Surg Volume 13, Number 2
radiocapitellar gap during elbow flexion after prosthetic radial head placement (Figures 4 and 5). The clinical and biomechanical data presented in this study indicate that overstuffing of the prosthesis in the radiocapitellar joint is a potential pitfall in the technique of radial head arthroplasty. The implant is routinely placed with the elbow in extension to facilitate broaching and stem placement. Although this position serves to prevent associated injury to the adjacent articular surfaces, it makes it critical to assess the fit of the prosthesis as the elbow is brought into full flexion. In addition, care must be taken to avoid eccentric broaching of the prostheses so as not to direct the prosthesis posterolaterally. Whereas there is the need for attention to detail in addressing the fit of the prosthesis in elbow flexion, there is also the issue of improved stability afforded in elbow extension. As with any arthroplasty technique, there is a balance between the enhanced stability seen with radial head arthroplasty versus the potential loss of motion, and an appropriate balance must be achieved. We thank Julia T. Rushing, MSTAT, for assistance with statistical analysis and E. Stanley Gordon, BS, for technical assistance with biomechanical testing. REFERENCES
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4. Fuchs S, Chylarecki C. Do functional deficits result from radial head resection? J Shoulder Elbow Surg 1999;8:247-51. 5. Harrington IJ, Sekyi-Otu A, Barrington TW, Evans DC, Tuli V. The functional outcome with metallic radial head implants in the treatment of unstable elbow fractures: a long-term review. J Trauma 2001;50:46-52. 6. Hotchkiss RN, An KN, Sowa DT, Basta S, Weiland AJ. An anatomic and mechanical study of the interosseous membrane of the forearm: pathomechanics of proximal migration of the radius. J Hand Surg [Am] 1989;14:256-61. 7. Hotchkiss RN. Displaced fractures of the radial head: internal fixation or excision? J Am Acad Orthop Surg 1997;5:1-10. 8. Hotchkiss RN. Fractures of the radial head and related instability and contracture of the forearm. Instr Course Lect 1998;47: 173-7. 9. King GJW, Zarzour ZDS, Rath DA, et al. Metallic radial head arthroplasty improves valgus stability of the elbow. Clin Orthop 1999;368:114-25. 10. Knight DJ, Rymaszewski LA, Amis AA, Miller JH. Primary replacement of the fractured radial head with a metal prosthesis. J Bone Joint Surg Br 1993;75:572-6. 11. Moro JK, Werier J, MacDermid JC, Patterson SD, King GJW. Arthroplasty with a metal radial head for unreconstructible fractures of the radial head. J Bone Joint Surg Am 2001;83:120211. 12. Morrey BF. Applied anatomy and biomechanics of the elbow joint. Instr Course Lect 1986;35:59-68. 13. Morrey BF, An KN, Stormont TJ. Force transmission through the radial head. J Bone Joint Surg Am 1988;70:250-6. 14. Morrey BF. Radial head fracture. In: Morrey BF, editor. The elbow and its disorders. 2nd ed. Philadelphia: Saunders; 1993. p. 383-404. 15. Rabinowitz RS, Light TR, Havey RM, et al. The role of the interosseous membrane and triangular fibrocartilage complex in forearm stability. J Hand Surg [Am] 1994;19:385-93. 16. Sellman DC, Seitz WH Jr, Postak PD, Greenwald AS. Reconstructive strategies for radio-ulnar dissociation: a biomechanical study. J Orthop Trauma 1995;9:516-22. 17. Skahen JR III, Palmer AK, Werner FW, Fortino MD. Reconstruction of the interosseous membrane of the forearm in cadavers. J Hand Surg [Am] 1997;22:986-94. 18. Werner FW, An KN. Biomechanics of the elbow and forearm. Hand Clin 1994;10:357-73.