- Email: [email protected]
Fatigue failure of a shoulder hemiarthroplasty stem: a case report
Fatigue failure of a shoulder hemiarthroplasty stem: A case report Joseph D. Zuckerman, Joel A. Shapiro, Sam Moghtaderi, and Frederick J. Kummer, New York, NY
A
mong the problems that have been reported with the stem of shoulder replacement prostheses are loosening and disassembly of modular components.1,4 The following is a case of prosthetic stem fatigue failure—a problem that has not been previously observed.
CASE REPORT A 47-year-old right hand– dominant man was seen at the orthopaedic clinic for evaluation of a 3-month history of severe right shoulder pain. Five years earlier, he had undergone a right shoulder hemiarthroplasty for posttraumatic arthritis and malunion after a proximal humerus fracture caused by a motor vehicle accident. After this initial procedure, he had controlled pain and limitation of motion and was involved in a chronic pain management program. Three months earlier, while at a hardware store, he was struck in the right arm by a piece of falling lumber. He had a significant increase in pain at that time; radiographs taken shortly thereafter revealed a fractured humeral prosthesis. Before presentation, he was managed with pain medications but received no definitive treatment. Physical examination revealed a healthy-appearing middle-aged man in no acute distress. Neurologic examination of the upper extremities was unremarkable. There was a well-healed anterior incision over the right shoulder, with a moderate amount of anterior deltoid and rotator cuff atrophy. There was no tenderness to palpation, although he did complain of pain with any movement. Passive rotation of the humerus caused pain and crepitus. Active range of motion consisted of forward elevation to 30°, external rotation to 20°, and internal rotation to the lumbosacral region. There was passive forward elevation to 90° with significant pain. Deltoid strength was 5/5, and external and internal rotation strength was 4/5. Radiographs revealed a fracture of the prosthetic stem at the junction of the proximal and middle thirds (Figure 1). The distal portion was well cemented in place, whereas the proximal part of the prosthesis lacked bony support. The tuberosities were displaced medially, superiorly, and posFrom the Shoulder Service, NYU–Hospital for Joint Diseases, Department of Orthopaedic Surgery. Reprint requests: Frederick J. Kummer, Musculoskeletal Research Center, Hospital for Joint Diseases, 301 E 17th St, New York, NY 10003. J Shoulder Elbow Surg 2003;12:635-6 Copyright © 2003 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/2003/$35.00 ⫹ 0 doi:10.1016/S1058-2746(03)00049-1
Figure 1 The failed prosthesis on initial patient presentation.
teriorly. Significant degenerative changes were also noted about the glenoid. A revision hemiarthroplasty was performed. The right shoulder joint was exposed by a deltopectoral approach. The proximal segment of the prosthesis was easily visualized and was noted to be freely mobile, requiring minimal dissection to remove. The distal stem segment that remained in the humeral shaft was removed by disrupting the cement mantle with multiple small drill holes. The remaining cement was removed with the use of an ultrasonic system. A modular proximal humeral prosthesis was then cemented into
635
636
Zuckerman et al
J Shoulder Elbow Surg November/December 2003
position. The tuberosities were mobilized and reattached with heavy nonabsorbable sutures. The area of bone loss over the proximal portion of the prosthesis was augmented with allograft. Two years postoperatively, the patient reported a significant reduction in pain but continued with a chronic pain management program consisting of Duragesic skin patches (Janssen Pharmaceutica, Titusville, NJ). His range of motion remained limited with active forward extension to 70°, external rotation to 20°, and internal rotation to the lumbosacral region. Radiographs showed that the implant was well fixed in the humerus but the tuberosities were displaced medially and posteriorly, similar to the preoperative position. The failed stem was a Depuy Global (Depuy, Warsaw, IN) titanium alloy, right modular humeral component. The stem failed immediately below an abrupt reduction in its cross-sectional area (Figure 2). Microscopic evaluation of the fracture surface revealed a typical fatigue fracture appearance with some evidence of burnishing resulting from movement that occurred after breakage. A fatigue crack grew across the implant as a result of repetitive loading until the remaining material was unable to resist an applied load and abruptly fractures. There were no obvious markings or machining marks on the stem that could have precipitated the fracture.
DISCUSSION The mechanism of failure of this humeral stem is similar to that observed with hip stems,3 in which a well-fixed, cemented distal stem is cantilever-loaded by an unsupported prosthetic head and proximal stem. This leads to fatigue of the stem at the supported region, crack growth, and failure by fracture when the remaining section of the stem is unable to resist an applied load—in this case the falling lumber. Although the loads on the humeral head are much lower than on the hip, they can approach body weight.2 The abrupt reduction in stem geometry acted as a stress concentrator and also acted to occlude cement in the medullar cavity, contributing to the lack of fixation support. Displacement of the tuberosities after the initial procedure added to this inadequate proximal support. This case suggests that particular care should be taken when smalldiameter humeral stems are used.
Figure 2 The failed stem with a fracture immediately below the reduced stem region.
REFERENCES
1. Klimkleiewicz JJ, Iannotti JP, Rubash HE, Shanbhag AS. Aseptic loosening of the humeral component in total shoulder arthroplasty. J Shoulder Elbow Surg 1998;7:422-6. 2. Poppen NK. Forces in the shoulder. In: Walker PS, editor. Human joints and their artificial replacements. Springfield (IL): C.C. Thomas; 1977. p. 87-94. 3. Woolson ST, Milbauer JP, Bobyn JD, Yue S, Maloney WJ. Fatigue
fracture of a forged cobalt-chromium-molybdenum femoral component inserted with cement. A report of ten cases. J Bone Joint Surg Am 1997;79:1842-8. 4. Zuckerman JD, Cavallo RJ, Kummer FJ. A review of the use of modularity in total shoulder arthroplasty. In: STP1301. Modularity of orthopedic implants. West Conshohocken (PA): American Society for Testing and Materials; 1997. p. 5–20.
A
mong the problems that have been reported with the stem of shoulder replacement prostheses are loosening and disassembly of modular components.1,4 The following is a case of prosthetic stem fatigue failure—a problem that has not been previously observed.
CASE REPORT A 47-year-old right hand– dominant man was seen at the orthopaedic clinic for evaluation of a 3-month history of severe right shoulder pain. Five years earlier, he had undergone a right shoulder hemiarthroplasty for posttraumatic arthritis and malunion after a proximal humerus fracture caused by a motor vehicle accident. After this initial procedure, he had controlled pain and limitation of motion and was involved in a chronic pain management program. Three months earlier, while at a hardware store, he was struck in the right arm by a piece of falling lumber. He had a significant increase in pain at that time; radiographs taken shortly thereafter revealed a fractured humeral prosthesis. Before presentation, he was managed with pain medications but received no definitive treatment. Physical examination revealed a healthy-appearing middle-aged man in no acute distress. Neurologic examination of the upper extremities was unremarkable. There was a well-healed anterior incision over the right shoulder, with a moderate amount of anterior deltoid and rotator cuff atrophy. There was no tenderness to palpation, although he did complain of pain with any movement. Passive rotation of the humerus caused pain and crepitus. Active range of motion consisted of forward elevation to 30°, external rotation to 20°, and internal rotation to the lumbosacral region. There was passive forward elevation to 90° with significant pain. Deltoid strength was 5/5, and external and internal rotation strength was 4/5. Radiographs revealed a fracture of the prosthetic stem at the junction of the proximal and middle thirds (Figure 1). The distal portion was well cemented in place, whereas the proximal part of the prosthesis lacked bony support. The tuberosities were displaced medially, superiorly, and posFrom the Shoulder Service, NYU–Hospital for Joint Diseases, Department of Orthopaedic Surgery. Reprint requests: Frederick J. Kummer, Musculoskeletal Research Center, Hospital for Joint Diseases, 301 E 17th St, New York, NY 10003. J Shoulder Elbow Surg 2003;12:635-6 Copyright © 2003 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/2003/$35.00 ⫹ 0 doi:10.1016/S1058-2746(03)00049-1
Figure 1 The failed prosthesis on initial patient presentation.
teriorly. Significant degenerative changes were also noted about the glenoid. A revision hemiarthroplasty was performed. The right shoulder joint was exposed by a deltopectoral approach. The proximal segment of the prosthesis was easily visualized and was noted to be freely mobile, requiring minimal dissection to remove. The distal stem segment that remained in the humeral shaft was removed by disrupting the cement mantle with multiple small drill holes. The remaining cement was removed with the use of an ultrasonic system. A modular proximal humeral prosthesis was then cemented into
635
636
Zuckerman et al
J Shoulder Elbow Surg November/December 2003
position. The tuberosities were mobilized and reattached with heavy nonabsorbable sutures. The area of bone loss over the proximal portion of the prosthesis was augmented with allograft. Two years postoperatively, the patient reported a significant reduction in pain but continued with a chronic pain management program consisting of Duragesic skin patches (Janssen Pharmaceutica, Titusville, NJ). His range of motion remained limited with active forward extension to 70°, external rotation to 20°, and internal rotation to the lumbosacral region. Radiographs showed that the implant was well fixed in the humerus but the tuberosities were displaced medially and posteriorly, similar to the preoperative position. The failed stem was a Depuy Global (Depuy, Warsaw, IN) titanium alloy, right modular humeral component. The stem failed immediately below an abrupt reduction in its cross-sectional area (Figure 2). Microscopic evaluation of the fracture surface revealed a typical fatigue fracture appearance with some evidence of burnishing resulting from movement that occurred after breakage. A fatigue crack grew across the implant as a result of repetitive loading until the remaining material was unable to resist an applied load and abruptly fractures. There were no obvious markings or machining marks on the stem that could have precipitated the fracture.
DISCUSSION The mechanism of failure of this humeral stem is similar to that observed with hip stems,3 in which a well-fixed, cemented distal stem is cantilever-loaded by an unsupported prosthetic head and proximal stem. This leads to fatigue of the stem at the supported region, crack growth, and failure by fracture when the remaining section of the stem is unable to resist an applied load—in this case the falling lumber. Although the loads on the humeral head are much lower than on the hip, they can approach body weight.2 The abrupt reduction in stem geometry acted as a stress concentrator and also acted to occlude cement in the medullar cavity, contributing to the lack of fixation support. Displacement of the tuberosities after the initial procedure added to this inadequate proximal support. This case suggests that particular care should be taken when smalldiameter humeral stems are used.
Figure 2 The failed stem with a fracture immediately below the reduced stem region.
REFERENCES
1. Klimkleiewicz JJ, Iannotti JP, Rubash HE, Shanbhag AS. Aseptic loosening of the humeral component in total shoulder arthroplasty. J Shoulder Elbow Surg 1998;7:422-6. 2. Poppen NK. Forces in the shoulder. In: Walker PS, editor. Human joints and their artificial replacements. Springfield (IL): C.C. Thomas; 1977. p. 87-94. 3. Woolson ST, Milbauer JP, Bobyn JD, Yue S, Maloney WJ. Fatigue
fracture of a forged cobalt-chromium-molybdenum femoral component inserted with cement. A report of ten cases. J Bone Joint Surg Am 1997;79:1842-8. 4. Zuckerman JD, Cavallo RJ, Kummer FJ. A review of the use of modularity in total shoulder arthroplasty. In: STP1301. Modularity of orthopedic implants. West Conshohocken (PA): American Society for Testing and Materials; 1997. p. 5–20.