JBJS | Fixation with Bioabsorbable Pins in Chevron Bunionectomy*

The Journal of Bone & Joint Surgery, Volume 79, Issue 10

Articles | October 01, 1997

Fixation with Bioabsorbable Pins in Chevron Bunionectomy*

LOWELL H. GILL, M.D.†; DAVID F. MARTIN, B.A.‡; JAMES M. COUMAS, M.D.‡; GARY M. KIEBZAK, PH.D.†, CHARLOTTE, NORTH CAROLINA

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Investigation performed at Miller Orthopaedic Clinic, Charlotte

The Journal of Bone & Joint Surgery. 1997; 79:1510-8

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Abstract

Fixation with bioabsorbable pins in distal chevron bunionectomy reduces the inconvenience and the risk of infection associated with fixation with stainless-steel Kirschner wires, which leaves a portion of the wires protruding from the skin. However, use of bioabsorbable implants has been reported to be associated with osteolysis and formation of a sinus with a sterile discharge. We studied the outcome and complications seen with use of poly-p-dioxanone pins and those seen with use of stainless-steel Kirschner wires after chevron bunionectomy in 114 patients (144 feet). We found no difference between the treatment groups with regard to the prevalence of complications or the stability of fixation. Notably, the prevalence of osteolysis was quite similar between the treatment groups; none of the feet that had had fixation with bioabsorbable pins had formation of a sinus with a sterile discharge. We believe that bioabsorbable pins can be used reliably to fix the site of the osteotomy for a distal chevron bunionectomy without undue risk of osteolysis or other complications.

Figures in this Article

Introduction

Introduction | Materials and Methods | Results | Discussion | References

Although distal chevron bunionectomy has been performed without fixation^{2,10,20,29,38}, many surgeons prefer to use fixation to reduce the likelihood of displacement of the osteotomy site and malunion^{12,14,18,19,25,28,30,33}. Fixation with Kirschner wires has been found to provide adequate stability³². However, such fixation for a bunion operation can be unpleasant for the patient. The wires may cause pain in the surrounding skin as well as unwanted skin traction, and they may provide a conduit for the introduction of bacteria to the operative area. Moreover, the wires limit the patient's ability to bathe because they usually should be kept dry. In addition, the range of motion at the metatarsophalangeal joints is limited in the early postoperative weeks because of irritation of the skin and pain associated with the tethering effect of the protruding wires during motion of the joint. Patients must avoid bumping or catching the wires on surrounding obstacles. Also, postoperative bunion splints are difficult to wear because of the protruding wires.

Fixation with bioabsorbable pins cut flush with the bone eliminates the inconvenience and the potential risks associated with protruding wires. However, use of bioabsorbable implants has been reported to be associated with osteolysis, synovitis, accumulation of fluid, extrusion of the implant, and formation of a sinus with sterile discharge^5-7. The prevalence of osteolysis associated with bioabsorbable implants has been reported by Böstman⁶ to be as high as 51 per cent (thirty-four of sixty-seven patients). Also, bioabsorbable implants are weaker than stainless-steel Kirschner wire¹¹, and the degradation of the pins in situ weakens them further²³. Potentially, therefore, the prevalence of failure of fixation is increased. The purpose of the present study was to evaluate the comparative risks associated with fixation with a bioabsorbable pin and those associated with traditional fixation with Kirschner wire in chevron bunionectomy.

*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.

†Miller Orthopaedic Clinic, 1001 Blythe Boulevard, Suite 200, Charlotte, North Carolina 28203.

‡Carolinas Medical Center, P.O. Box 32861, Charlotte, North Carolina 28232.

*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.

†Miller Orthopaedic Clinic, 1001 Blythe Boulevard, Suite 200, Charlotte, North Carolina 28203.

‡Carolinas Medical Center, P.O. Box 32861, Charlotte, North Carolina 28232.

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TABLE I DATA ON THE PATIENTS*

*There were no significant differences, as determined with the two-tailed unpaired t test, between the groups with regard to the demographic variables.†The values are reported as the mean and standard deviation.‡Significantly different (p < 0.0001) from the preoperative mean, as determined with the two-tailed paired t test.§Significantly different (p = 0.0004) from the value for the group that had fixation with Kirschner wires, as determined with the two-tailed unpaired t test.#Significantly different (p = 0.0063) from the value for the group that had fixation with Kirschner wires, as determined with the two-tailed unpaired t test.**Significantly different (p = 0.0033) from the value for the group that had fixation with Kirschner wire, as determined with the two-tailed unpaired t-test.

					Intermetatarsal Joint Angle		Metatarsophalangeal Joint Angle
Group	Patients/ Feet (No.)	Men/ Women (No.)	Age† (Yrs.)	Pins per Foot† (No)	Preop.† (Degrees)	Postop.† (Degrees)	Change (Per cent)	Preop† (Degrees)	Postop.† (Degrees)	Change (Per cent)
Bioabsorbable pins	59/70	4/55	48 ± 15	1.9 ± 0.5	11.1 ± 2.5‡	5.8 ± 2.3§	-48	23.8 ± 6.8	9.0 ± 5.0§**	-62

Kirschner wires	59/74	6/53	48 ± 17	2.1 ±1.1	12.9 ± 3.4	6.4 ± 1.9§	-50	27.5 ± 9.0	11.7 ± 5.8§	-57

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TABLE I DATA ON THE PATIENTS*

					Intermetatarsal Joint Angle		Metatarsophalangeal Joint Angle
Group	Patients/ Feet (No.)	Men/ Women (No.)	Age† (Yrs.)	Pins per Foot† (No)	Preop.† (Degrees)	Postop.† (Degrees)	Change (Per cent)	Preop† (Degrees)	Postop.† (Degrees)	Change (Per cent)
Bioabsorbable pins	59/70	4/55	48 ± 15	1.9 ± 0.5	11.1 ± 2.5‡	5.8 ± 2.3§	-48	23.8 ± 6.8	9.0 ± 5.0§**	-62

Kirschner wires	59/74	6/53	48 ± 17	2.1 ±1.1	12.9 ± 3.4	6.4 ± 1.9§	-50	27.5 ± 9.0	11.7 ± 5.8§	-57

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Fig. 1 Drawing showing placement of the two poly-p-dioxanone pins (1 and 2) for fixation in the chevron bunionectomy.

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Fig. 2 Drawing showing placement of the two stainless-steel Kirschner wires (1 and 2) for fixation in the chevron bunionectomy.

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Figs. 3-A and 3-B: Anteroposterior radiographs of a foot that was treated with a chevron bunionectomy fixed with bioabsorbable pins as described in the text. Fig. 3-A: Preoperative radiograph showing the intermetatarsal and metatarsophalangeal angles.

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Fig. 3-B: Radiograph made four months after the bunionectomy, showing mild osteolysis (arrow) associated with the poly-p-dioxanone pins.

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Fig. 4 Radiograph made three months after a chevron bunionectomy fixed with Kirschner wires, showing mild osteolysis.

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Fig. 5 Radiograph made two months after a chevron bunionectomy fixed with Kirschner wires, showing more severe osteolysis due to osteomyelitis.

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Figs. 6-A and 6-B: Radiographs of one of the three feet in which severe osteolysis developed after a chevron bunionectomy fixed with bioabsorbable pins. Fig. 6-A: Two months postoperatively, the severe osteolysis was evident.

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Fig. 6-B: Nine months postoperatively, the osteolysis had resolved. A healing stress fracture of the second metatarsal was also seen.

Materials and Methods

Introduction | Materials and Methods | Results | Discussion | References

One of us (L. H. G.) performed 144 chevron bunionectomies in 114 patients with use of the same preoperative care, operative technique (with the exception of the type of fixation), and postoperative care (with the exception of the care of the fixation devices) for all patients. In 1992, we began the transition from fixation with stainless-steel Kirschner wires to the present technique of fixation with bioabsorbable poly-p-dioxanone pins (Orthosorb; Johnson and Johnson Orthopaedics, Raynham, Massachusetts) because we believed that the use of bioabsorbable pins was preferable to fixation with Kirschner wires. However, because the pins were inconsistently available to us until 1994, patients were managed with either stainless-steel Kirschner wires or bioabsorbable pins throughout 1992 and 1993. We report the outcome for the first fifty-nine patients (seventy feet) who had fixation with bioabsorbable pins and compare it with that for fifty-nine consecutive patients (seventy-four feet) who had fixation with Kirschner wires during approximately the same time-period. Four of the patients who had a bilateral bunionectomy had fixation with bioabsorbable pins in one foot and Kirschner wires in the other; thus, there was a total of 114 patients (144 feet).

There were no differences between the two groups with respect to the age and gender of the patients or the number of pins used (Table I).

Operative Indications and Technique

The primary indication for bunionectomy in the present series was pain over a medial bunion that made walking and wearing shoes uncomfortable. Patients who had mild-to-moderate metatarsus primus varus with an intermetatarsal angle of 16 degrees or less and who had no radiographic evidence of metatarsophalangeal arthrosis were considered candidates for the procedure, regardless of age. Furthermore, patients who were found to have only mild-to-moderate tightness of the adductor tendon on clinical examination were accepted for the present study because adductor tenotomy was not performed in combination with distal chevron bunionectomy. If adductor tenotomy was believed to be advisable because of a tight adductor tendon on clinical examination, the patient was managed with a proximal osteotomy and distal realignment. Such patients were excluded from the present study.

A medial incision is used at the metatarsophalangeal joint. The underlying joint capsule is incised in a Y-shaped fashion, with the V-shaped flap reflected distally, exposing the medial prominence of the metatarsal head. After removal of the medial exostosis, a chevron-shaped osteotomy is fashioned in the metatarsal neck with use of an oscillating saw with a small blade. The two bone cuts are made more horizontally than has been described in earlier reports^10,20. A longer, more horizontal osteotomy maximizes the surface area for opposition, enhances stability, and provides more area for placement of the pins (Figs. 1 and 2). The resultant angle at the apex of the proximal fragment is approximately 35 degrees. This type of cut also minimizes the risk to the circulation of the metatarsal head²¹. A small thin osteotome is used to help free the deeper part of the osteotomy and then is used as a lever to gently displace the distal fragment laterally. The displacement is one-quarter to one-third the width of the metatarsal neck (usually three to five millimeters), and it is transfixed with two pins placed through separate non-parallel stab wounds in a dorsal-to-plantar direction (Figs. 1 and 2). The proximal bone fragment is shaved flush with the displaced distal fragment, and the medial aspect of the capsule is shortened and then repaired, correcting the hallux valgus.

Fixation was achieved with either two 0.062-inch (1.574-millimeter) stainless-steel Kirschner wires or two 1.3-millimeter bioabsorbable pins. The 1.3-millimeter-diameter bioabsorbable pins are attached to a metal pin of the same diameter, providing the necessary strength for insertion with a power drill. After initial placement of the pin and withdrawal of the metal pin from below, the bioabsorbable segment of the pin is drawn across the site of the osteotomy (Fig. 1). The bioabsorbable pins are cut flush with the bone and are left in place. The Kirschner wires are left protruding through the dorsal skin, are covered with Jurgan pin balls (DePuy Manufacturing, Charlotte, North Carolina) to prevent the wires from catching on clothing, and are wrapped with Xeroform gauze (Kendall Healthcare Products, Mansfield, Massachusetts) and sterile dressing. The wires are left in place for five to six weeks and then are removed without anesthesia during an office visit.

Postoperative Care

A sterile bulky dressing was used for ten to twelve days, after which the dressing and sutures were removed and 0.25-inch (6.35-millimeter) Steri-Strips (3M, St. Paul, Minnesota) were applied over dried benzoin. The patients who had fixation with Kirschner wires were instructed to keep them dry and dressed with sterile gauze. All patients were advised to report any problems with the wound or with healing. All patients wore postoperative wooden-soled shoes for six weeks and then as needed. The patients were given a cloth bunion splint for walking and a firm bunion splint for nighttime use. We suspect that there was less compliance with use of the postoperative splints in the group that had fixation with Kirschner wires as the splints were difficult to wear around the protruding wires. All patients were allowed weight-bearing as tolerated beginning on the day of the operation. Full-time bed rest was encouraged for the first postoperative week, and bed rest for 50 per cent of the waking hours was recommended for the second week. After two weeks, the patients were allowed to walk as much as they wanted.

After the initial visit for removal of the sutures, at ten to twelve days postoperatively, the patients were evaluated clinically at six weeks, three months, six months, and one year. Wound-healing was assessed clinically at these intervals and at additional visits, if necessary, to care for the wound.

Poor healing was defined as a wound with abnormal discoloration, clear drainage, or necrosis of the margin. When a wound appeared erythematous and there was no drainage or clinical suspicion of infection, it was defined as erythematous, in contrast to a wound with purulent drainage, which was defined as infected.

Radiographic Review

The radiographs made preoperatively and at each follow-up visit were reviewed independently by a radiologist (J. M. C.) who was blinded to the technique of fixation. The radiographs made ten to twelve days postoperatively were omitted from the review, and the six-week radiographs were made after removal of the pins to assist in the blinding of the review. The correction of the intermetatarsal angle between the first and second metatarsal joints and the correction of the metatarsophalangeal joint angle were measured in both treatment groups (Fig. 3-A). Radiographic assessment of the fixation site included measurement of the diameter of the pin track and documentation of sharp, distinct, geographic osseous margination. Sequential radiographs were assessed for any enlargement of the pin track, loss of distinct margination, or osseous resorption at the site of the pin track. Any degree of osteolysis, even mild osteolysis, as well as the position of the fixed osteotomy fragments, preoperative and postoperative correction, and loss of fixation were evaluated. Osteolysis was considered to be mild if the area of involvement measured five millimeters or less (Figs. 3-B and 4) and to be more severe if it measured more than five millimeters (Figs. 5, 6-A, and 6-B). After the independent review by the radiologist, a retrospective review was done of the charts of all patients who had radiographic evidence of osteolysis. The prevalence of infection in these patients and the clinical outcome were correlated with the radiographic findings.

Results

Introduction | Materials and Methods | Results | Discussion | References

The prevalence of osteolysis was essentially identical in the two groups. The radiologist noted osteolysis in five feet that had had fixation with Kirschner wires. The osteolysis was mild in two feet (Fig. 4), which did not have an infection and were not treated with antibiotics. The osteolysis in the remaining three feet was more serious, with the area of involvement measuring more than five millimeters (Fig. 5). Postoperatively, those three feet were noted by the clinician to have a draining wound that was considered to be infected and they had radiographic evidence of osteomyelitis. The three patients were given antibiotics for a period of four to six weeks, and all had complete resolution of the infection on clinical examination. Minor degenerative changes developed in the lateral aspect of the metatarsophalangeal joint in one foot. All five feet that had radiographic evidence of osteolysis had complete resolution of the lesion within twelve months.

Of the fifty-nine patients who were managed with the bioabsorbable pins, six were found to have osteolysis. None of the six feet had formation of a sinus with a sterile discharge. Three of the six had mild osteolysis (Fig. 3-B), and three had more severe osteolysis (Fig. 6-A). The osteolysis was observed to follow the pin track (Figs. 6-A and 6-B) in all six feet, but only one of the feet had wound drainage. This drainage was slight, and there was scant growth of Staphylococcus epidermidis on culture. That patient and one additional patient were given antibiotics for one to four weeks during the postoperative period because of concern about erythema of the wound. No antibiotics were given to the other four patients. All six patients had complete resolution of the osteolysis relative to the pin track during a period of four to eighteen months. An anteroposterior radiograph revealed development of a painless, stable non-union in one patient, and the lateral radiograph showed minimum bone-bridging dorsally. The osteolysis persisted, but it was judged to be secondary to the non-union rather than to the bioabsorbable pins.

The three patients who had an infection in association with Kirschner wires returned for a total of five extra follow-up visits for care of the wound. In addition to the three infections, problems with wound-healing were more apparent in the patients who were managed with Kirschner wires. Five patients (five feet) in that group compared with one who had fixation with the bioabsorbable pins were noted on clinical examination to have poor healing of the wound.

The two groups were similar with regard to the occurrence of other complications. These complications included shortening (one foot in each group), loss of fixation (one foot treated with pins compared with three feet treated with wires), postoperative degenerative arthrosis of the metatarsophalangeal joint (three feet treated with wires), erythema of the wound (seven feet treated with pins compared with eight feet treated with wires), and malunion of the osteotomy (one foot treated with pins).

The preoperative intermetatarsal and metatarsophalangeal joint angles were slightly but significantly smaller in the group that had fixation with bioabsorbable pins (p = 0.0004 and p = 0.0063, respectively) compared with those in the group that had fixation with Kirschner wires (Table I). The magnitude of the change in the intermetatarsal and metatarsophalangeal joint angles after the operation was similar and significant (p < 0.0001) in both groups.

Discussion

Introduction | Materials and Methods | Results | Discussion | References

The most commonly cited advantages of bioabsorbable implants are the elimination of the need for removal of hardware and its related cost⁹ as well as the gradual transfer of stress to bone^15,26. Skin care also is simplified, and postoperative wounds may be kept closed without the need for later removal of the pins. Patients are more comfortable in the early postoperative period, and splinting is easier. The two main potential disadvantages are the possible loss of mechanical stability and the biological reaction of the host to the implant.

As bioabsorbable implants are mechanically weaker than metallic devices and since they lose strength progressively with hydrolysis as well as degradation^23,26, they are considered by some to be best in applications associated with low load as well as rapid healing and for fixation of small bone fragments⁹. The poly-p-dioxanone pins used in the present study have been used successfully in the treatment of osteochondral fractures, both clinically and experimentally²⁸. However, they have been shown to be mechanically inferior to polylactic acid malleolar screws and ASIF cannulated screws (Synthes, Paoli, Pennsylvania) for the fixation of Salter-type physeal fractures in laboratory animals¹¹. Also, roentgen stereophotogrammetric analysis has shown that metallic fixation provides better stability for the fixation of fractures¹.

The osteotomy site in the shape of a chevron is inherently more stable when oriented perpendicular to the plane of stress than a linear or curved osteotomy performed parallel to the plane of stress (such as a distal Mitchell osteotomy distally or a crescentic osteotomy at the proximal base of the first metatarsal). Furthermore, patients undoubtedly tend to unload the area by bearing more weight initially on the heels. Despite the greater stability of the site of a chevron osteotomy, the need for fixation has been documented^{12,14,17,18,22,24,25,28,30,33}. Loss of fixation has been reported when the procedure has been performed without fixation^{12,14,17,18,22,24,33}. Donnelly et al. suggested that the technique be modified by using a single screw¹². Shereff et al. showed that pin fixation provides acceptable stability³².

Loss of fixation is possible after removal of the Kirschner wires. This occurred in three of our patients and was associated with varus angulation of the distal fragment of 15, 20, and 25 degrees. The loss of fixation may have been secondary to the tight repair of the medial capsule and the early removal of the Kirschner wires. We occasionally have seen patients who had an erythematous-appearing wound before the scheduled follow-up visit for removal of the wires at five to six weeks. Because of concern about infection, there is a tendency to remove the wires early, as early as three weeks postoperatively in some instances³⁸. At that point, all non-biological fixation is terminated.

There is no abrupt loss of fixation with bioabsorbable pins. Instead, there is a gradual transfer of stress to bone. The strength of the poly-p-dioxanone material remaining at four weeks has been reported to be 50 to 70 per cent^11,16,37 of the strength at the time of insertion, with 25 per cent remaining at six weeks¹¹. A study of 1.3-millimeter-diameter poly-p-dioxanone pins implanted in the femora of mature rabbits showed that the strength of the pins was more than 80 per cent at four weeks and 55 per cent at five weeks⁴.

The metaphysis is considered an ideal location for bioabsorbable implants because the pins do not perform as well in diaphyseal locations⁹. A metaphyseal location also is favorable for healing. Furthermore, the chevron shape, in addition to improving stability, increases the surface area for healing. Therefore, the chevron bunionectomy, when performed in a metaphyseal location, may be the ideal procedure with which to use a bioabsorbable implant. However, as fixation with these pins should be limited to areas of minimum stress, they should not be used in a more proximal location or in a major fracture of the foot.

The biological response of the host to synthetic polymers also is an important consideration. Although usually well tolerated, polyglycolic acid implants have been associated with osteolysis in many reports^5-7,13. Hydrolysis causes the implants to disintegrate into smaller fragments, which may stimulate a foreign-body reaction^5,34. If the reaction is intense, it may be associated with erythema, pain, swelling, local accumulation of fluid that may need to be drained, or even the formation of a draining sinus^5,8,18,34. The drainage fluid typically is sterile on culture^5,11,18. In bone, the local inflammatory reaction may be associated with transient osteolysis that resolves during a period of months. When osteolysis with a draining sinus has been observed, it has been associated most often with polyglycolic acid implants, not the poly-p-dioxanone material used in the present study^1,5-7,13.

To our knowledge, osteolysis associated with poly-p-dioxanone has been reported in only one other study³³. In that study, osteolysis developed in four of seventy-one feet after a distal chevron bunionectomy that was fixed with poly-p-dioxanone pins; this finding was similar to that in our study, in which three patients had mild osteolysis (Fig. 3-B). However, the more severe osteolysis associated with poly-p-dioxanone pins, which developed in three patients in our study, has not been reported previously to our knowledge.

The rate of degradation, size of the implant, specific anatomical area, presence of contrast medium in the implant, number of bone portals (single or double), and age of the patient have been proposed as the factors that affect the prevalence of inflammatory reaction or osteolysis.

The rate of degradation has been considered a potentially important factor in the development of adverse tissue reactions because the volume of breakdown products per unit of time in local surrounding tissues is greater for an implant that degrades rapidly, such as a polyglycolic acid device, than for an implant of the same size that degrades more slowly, such as one made of polylactic acid^9,16. Most reports of adverse tissue reaction have involved polyglycolic acid^{1,4-6,13,15,18,35}, which degrades over a period of a few months^3,6. In contrast, polylactic acid is completely resorbed over a period of one and one-half to four years³. Although inflammatory reactions associated with slowly degrading polymers such as polylactic acid have been reported only rarely^5,8, it should be noted that there are comparatively few studies on the use of polylactic acid implants⁵. Therefore, the prevalence of inflammatory reactions or osteolysis with polylactic acid may be underestimated at present.

The time until degradation of the poly-p-dioxanone pins used in the present study, although longer than that for comparably sized polyglycolic acid implants, is still relatively short. The poly-p-dioxanone pin loses all of its strength by two months, and there is total resolution at six months^3,26. With respect to the rate of degradation alone, therefore, one might expect adverse tissue reactions with poly-p-dioxanone. However, in addition to the osteolysis seen in six (9 per cent) of the seventy feet that had fixation with a poly-p-dioxanone pin in our study, Small et al.³³ are the only other authors who reported similar reactions to poly-p-dioxanone, to our knowledge. They noted that osteolysis developed in four (6 per cent) of seventy-one feet in which the Orthosorb bioabsorbable pin was used in a chevron bunionectomy³³.

Pins with a smaller diameter and a greater surface area per unit of mass degrade more quickly²³. Thus, small-diameter pins have been associated with foreign-body reactions and osteolysis^13,18,33. In a study of children, Frasier and Cole¹³ noted osteolysis in three of twenty-one elbows in which a fracture had been fixed with thin 1.5-millimeter and 2.0-millimeter-diameter polyglycolic acid pins.

The amount of stress also may influence the rate of degradation of resorbable polymers⁹. High stress accelerates degradation. Therefore, the diaphysis of a large bone is a less suitable location for resorbable implants than the metaphysis of a small bone.

Differences in degradation also depend on a number of factors involving the specific polymer being used. In addition to molecular weight, mass, and strength, the porosity, crystallinity, hydrophobicity or hydrophilicity, and thermal history also influence degradation kinetics³¹. For example, the 1.3-millimeter-diameter bioabsorbable pin used in the present study has been shown to have a slower rate of degradation than a 2.0-millimeter-diameter pin made of the same polymer because the smaller pin had increased crystallinity³¹.

Böstman⁵ noted that the inflammatory reaction associated with a bioabsorbable implant is more prevalent in specific anatomical areas. For example, an inflammatory reaction was seen in 25 per cent (five) of twenty scaphoids compared with 7 per cent (three) of forty-one ankles⁵. Hirvensalo et al. reported an inflammatory reaction in 3 per cent (two) of seventy-eight feet in which the site of a chevron osteotomy of the first metatarsal had been fixed with polyglycolic acid pins¹⁸. Two of the patients in that study also had formation of a sinus with a sterile discharge. Some of the most severe inflammatory reactions have been associated with an intraarticular location of the fracture³⁴.

The specific type of tissue into which the pin is implanted also has been noted to influence degradation kinetics. DL-polylactic acid implants have been noted to degrade more rapidly when placed subcutaneously rather than subperiosteally³⁶, whereas poly-p-dioxanone pins have been found to degrade more rapidly in the medullary canal than in muscle or subcutaneous tissue⁴.

Böstman speculated that when a polyglycolide rod is associated with a single bone portal, the prevalence of osteolysis may increase⁶. More osteolysis is seen in the deepest part of an implant channel⁶, implying that degradation products need to exit the bone if osteolysis is to be prevented. In our study, all patients had a double (dorsal and plantar) portal through cortical bone. This double portal might allow the egress of degradation products from bone over a larger area of periosteal soft tissue and might help to explain the low prevalence of osteolysis. However, in the study by Frasier and Cole¹³, obvious osteolysis developed, despite the presence of two portals, in three children after fixation of a fracture with polyglycolic acid pins.

Orthosorb pins contain a non-reactive dye (D and C Violet number 2) that was approved by the Food and Drug Administration. Some studies have shown that the presence of a dye influences foreign-body reaction and osteolysis^7,35. Böstman et al.⁷ reported that the prevalence of foreign-body reactions was markedly higher in patients who had fixation with first-generation screws colored with an aromatic quinone dye (nineteen reactions in 105 patients) than in those who had fixation of a malleolar fracture with non-colored 4.5-millimeter polyglycolic acid screws (five reactions in 111 patients).

Histological studies of the reaction of the host to poly-p-dioxanone in a rabbit model demonstrated an initial inflammatory reaction after implantation²⁶. The reaction was followed three weeks postoperatively by the formation of new bone, which has been termed a bone cuff, surrounding the poly-p-dioxanone implant. It has been postulated that this bone cuff may enhance the longevity of the poly-p-dioxanone pin by retarding resorption⁴. However, by twenty-four weeks postoperatively, marked thinning and loss of osseous trabeculae were observed around the pin²⁶.

Conversely, no inflammatory reaction associated with poly-p-dioxanone pins was observed in a study in goats¹¹. Instead, the pin was surrounded by a layer of fibrous tissue that was thicker than that seen with polylactic acid screws or ASIF metallic screws in the same animals¹¹. Also, differences in the tissue response to bioabsorbable polymers have been noted between humans and laboratory animals⁶.

In summary, osteolysis, which is frequently found in association with polyglycolic implants, was observed in six of our fifty-nine patients who had had fixation of the site of a distal chevron bunionectomy with smaller (1.3-millimeter-diameter) bioabsorbable poly-p-dioxanone pins. However, the osteolysis was a radiographic observation only—it was not associated with clinical complications—and it was no more frequent than that seen with traditional Kirschner wires. Also, none of the biodegradable pins were associated with severe inflammatory reactions accompanied by the formation of a sinus with a sterile discharge, as has been seen with larger polyglycolic acid implants. Moreover, the osteolysis resolved in all six patients, without the use of antibiotics in five of them. With the possible exception of problems with the wound in the patients who had fixation with Kirschner wires, the two groups in our study had very similar complications. In addition, the disadvantages related to protrusion of the Kirschner wires through the skin were avoided with use of bioabsorbable pins.

NOTE: The authors thank Kevin Cuthbertson and Timothy Re, teachers involved in the Scientist-Teacher Exchange Program who worked for them during the summer of 1994, for their help with compilation of the data.

References

Introduction | Materials and Methods | Results | Discussion | References

Ahl, T.; Dalen, N.; Lundberg, A.; and Wykman, A.: Biodegradable fixation of ankle fractures. A roentgen stereophotogrammetric study of 32 cases. Acta Orthop. Scandinavica,65: 166-170, 1994.65166 1994

Austin, D. W., and Leventen, E. O.: A new osteotomy for hallux valgus: a horizontally directed "V" displacement osteotomy of the metatarsal head for hallux valgus and primus varus. Clin. Orthop.,157: 25-30, 1981.15725 1981 [PubMed]

Barrows, T. H.: Degradable implant materials: a review of synthetic absorbable polymers and their applications. Clin. Mater.,1: 233-257, 1986.1233 1986

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Fig. 1 Drawing showing placement of the two poly-p-dioxanone pins (1 and 2) for fixation in the chevron bunionectomy.

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Fig. 2 Drawing showing placement of the two stainless-steel Kirschner wires (1 and 2) for fixation in the chevron bunionectomy.

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Fig. 3-B: Radiograph made four months after the bunionectomy, showing mild osteolysis (arrow) associated with the poly-p-dioxanone pins.

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Fig. 4 Radiograph made three months after a chevron bunionectomy fixed with Kirschner wires, showing mild osteolysis.

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Fig. 5 Radiograph made two months after a chevron bunionectomy fixed with Kirschner wires, showing more severe osteolysis due to osteomyelitis.

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Fig. 6-B: Nine months postoperatively, the osteolysis had resolved. A healing stress fracture of the second metatarsal was also seen.

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TABLE I DATA ON THE PATIENTS*

					Intermetatarsal Joint Angle		Metatarsophalangeal Joint Angle
Group	Patients/ Feet (No.)	Men/ Women (No.)	Age† (Yrs.)	Pins per Foot† (No)	Preop.† (Degrees)	Postop.† (Degrees)	Change (Per cent)	Preop† (Degrees)	Postop.† (Degrees)	Change (Per cent)
Bioabsorbable pins	59/70	4/55	48 ± 15	1.9 ± 0.5	11.1 ± 2.5‡	5.8 ± 2.3§	-48	23.8 ± 6.8	9.0 ± 5.0§**	-62

Kirschner wires	59/74	6/53	48 ± 17	2.1 ±1.1	12.9 ± 3.4	6.4 ± 1.9§	-50	27.5 ± 9.0	11.7 ± 5.8§	-57

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TABLE I DATA ON THE PATIENTS*

					Intermetatarsal Joint Angle		Metatarsophalangeal Joint Angle
Group	Patients/ Feet (No.)	Men/ Women (No.)	Age† (Yrs.)	Pins per Foot† (No)	Preop.† (Degrees)	Postop.† (Degrees)	Change (Per cent)	Preop† (Degrees)	Postop.† (Degrees)	Change (Per cent)
Bioabsorbable pins	59/70	4/55	48 ± 15	1.9 ± 0.5	11.1 ± 2.5‡	5.8 ± 2.3§	-48	23.8 ± 6.8	9.0 ± 5.0§**	-62

Kirschner wires	59/74	6/53	48 ± 17	2.1 ±1.1	12.9 ± 3.4	6.4 ± 1.9§	-50	27.5 ± 9.0	11.7 ± 5.8§	-57