Multicenter Trial of Modified Gamma Nail in East Asia

Abstract

The mismatch of the standard Gamma nail in the Chinese femora led to the modification of its femoral shaft component based on the anthropometric study of 28 pairs of Chinese femora. A multicenter clinical trial was done in 6 countries and regions in East Asia. Three hundred forty-nine fractures were treated and studied. More than 60% of the fractures were unstable by Evans classification. The average age of the patients was 73.6 years. The male to female ratio was 2:3. The mean followup period was 11.7 months. The result of the trial showed that the intraoperative complication rate was 7.7%, and complications primarily were related to faulty operative technique. There were 7.2% postoperative complications related to the fractures that again decreased toward the later stage of the trial. Functionally, there was progressive improvement of the hip score within the followup period. The results show that the modified Gamma nail gave better results in the treatment of geriatric trochanteric fractures by minimizing reaming, thereby reducing complications related to the implants.

The treatment of peritrochanteric fractures of femora with the Gamma nail has the theoretic advantages of combining the merits of intramedullary fixation and the sliding screws. However, the clinical results have not clearly established^3,5,12,19,23 the assumptions. In a previous report, the authors have identified that 1 cause for the intraoperative and postoperative complications is the mismatch of the configuration of the nail to the geometry of the proximal femur in Asian patients.¹⁸ To improve the design of the femoral shaft component of the nail, an anthropometric study of the proximal femora of Chinese individuals was done. The result of the anthropometric study was applied to the modification the femoral shaft component of the Gamma nail (Fig 1, Table 1). With this new component of the nail and with a modified operative technique, a multicenter clinical trial was done in East Asia.

MATERIALS AND METHOD

The surgeons from the trial centers met in July 1991, and the treatment protocol and operative technique were standardized. Three subsequent interim meetings were held during the early trial period to monitor the progress and modify the protocol. All of the clinical data and radiographs were sent to Hong Kong, the monitoring center for supervision and data analysis.

Patients older than 60 years of age with peritrochanteric fractures were included in this study. Their premorbid conditions were recorded. Fractures were classified anatomically as peritrochanteric or intertrochanteric with or without subtrochanteric extension. Fracture stability was assessed by the methods of Evans⁷ as modified by Jensen.¹⁴

The operation was done with the patient given general or spinal anesthesia with prophylactic antibiotic cover. Immediate mobilization and weightbearing walking were allowed as soon as the patient's condition permitted. Patients were discharged from the hospital when independent walking with or without aids became possible. Postoperative followup visits were made at 6 weeks, 3 months, 6 months, and then every 6 months. Radiographs were taken in each followup visit.

Clinical assessment included postoperative walking ability, the Charnley Hip Score, fracture healing, and radiologic measurement of the sliding of the lag screw,¹⁵ and intraoperative and postoperative complications were recorded with respect to the implants, fractures, and patients. The geometric configuration of the femoral component was matched with the proximal femur on radiographs in all cases.

Modification of the Femoral Shaft Component

According to the results from the anthropometric study,¹⁷ the modified nail has the standard length of 180 mm, distal diameter of 11 or 12 mm, mediolateral angle of 4 °, neck shaft angle of 130 °, and the axis of the lag screw hole moved 10 mm distal from the average center axis of the greater trochanter.

Modification of Operative Technique

For the modified nail, the operative technique was additionally modified.¹⁶

Minimal intramedullary reaming was recommended with the modified nail. After the entry hole was made with the awl at the tip of the greater trochanter, a guide wire was passed, and the nail of the estimated size was inserted. If difficulty was encountered, a nail with a smaller diameter was inserted. Reaming was done only when difficulty was encountered with the insertion of the 11-mm nail. All insertions were done manually without hammering.

For the modified nail, the lag screw was designed to be positioned in the inferior ½ of the femoral neck and head. Thus, the nail should be inserted to the proper depth before targeting the lag screw.

Distal locking was done in all unstable fractures and those with rotational instability caused by a large medullary canal diameter. Targeting always was started with the proximal locking screw. With the outer sleeve in place, the awl was used to create a small depression by gentle hammering on the lateral cortex to centralize the drill bit. The awl should never penetrate the cortex of the femur. With the second sleeve inserted, the femur was drilled with a 5.5-mm drill bit. A fully threaded 6.28-mm cross screw with the correct length was inserted. With the screw driver still engaging the screw head, the targeting of the distal screw was done by repeating the procedures (Fig 2).

RESULTS

From October 1991 to October 1993, 349 patients were included in the study (Fig 3). There were 145 men and 204 women. Their ages ranged from 58 to 96 years, with an average of 73.6 years (Fig 4). The general condition of these patients was reflected from the anesthetic risk scoring according to the American Society of Anesthesiologists⁶(Fig 5). Before the injury, 21.2% of the patients had disability in mobility. One hundred sixty-four fractures occurred on the right side and 187 on the left side. There were 122 stable fractures and 227 unstable fractures (Fig 6). Thirty-three fractures had subtrochanteric extensions. The bone quality of the contralateral hip was assessed according to the osteoporosis Singh index: this information is shown in Figure 7.

The duration of the operation ranged from 25 to 155 minutes, with an average of 58 minutes. The duration of radiographic screening for reduction of the fracture ranged from 0 to 368 seconds, with an average of 22 seconds, and the duration of operative radiographic screening ranged from 6 to 168 seconds, with an average of 113 seconds. The need for reaming is presented in Table 2. Of the fractures, 58.5% were fixed with less reaming than would be used with the recommended technique.¹¹ The size of the lag screws used is shown in Figure 8. The screw sizes most frequently used were 90 mm and 100 mm. With regard to the position of the lag screw in the frontal view of the hip, 228 (65.3%) fractures were fixed with the lag screws in the inferior ½ of the femoral neck and head, 52 (14.9%) were fixed in the center, and 69 (19.8%) were fixed in the superior ½. On the lateral view, 261 (74.8%) were in the center, 25 (7.2%) were anterior, and 63 (18%) were posterior (Fig 9). Ninety (25.8%) fractures were fixed without distal locking, 63 (18.1%) with 1 screw, and 196 (56.1%) locked with 2 screws.

Postoperative drainage ranged from 5 to 810 ml, with an average of 130 ml. Blood transfusion was done in 136 (38.9%) patients, and the volume transfused ranged from 450 to 1500 ml, with an average of 550 ml.

Postoperatively, 41 (11.8%) patients died within the first 6-month period. Two hundred sixty-four (75.6%) patients completed the 6-month followup, and 220 (63%) patients had a followup period longer than 6 months. The followup period ranged from 6 to 19 months, with an average of 11.7 months. The analysis of the clinical and radiologic results are based on these patients.

At 6 months of followup, 99 patients walked without aids, 133 patients required crutches or a cane for walking, and 32 patients could not walk. The hip function as assessed by the Charnley Scoring System showed that the average pain score was 4.39, the average functional score was 3.82, and the average score for motion was 4.90. At the last followup visit that the patients attended, 97 patients walked independently, 108 patients required aids for walking, and 15 patients were bed or chair bound. The Charnley Hip Score showed that the average pain score was 5.21; the average functional score was 4.23, and the average motion score was 5.13.

Radiologic assessment showed that at 6 months of followup, 221 fractures healed, and at the final followup, all fractures healed. The range of the sliding of the lag screws was between 0 and 18.9 mm, with an average of 5.96 mm. The relationship of the femoral shaft component to the femora is shown in Figure 10.

Complications

The intraoperative complications are presented in the Table 3. The major complications are listed, whereas the minor complications were those that did not require an additional procedure and did not affect the fracture fixation or the clinical outcome. The general complications occurred immediately after the operation and are shown in Table 4. These were related to the patients' general conditions. The local complications related to the injured hip are presented in Table 5. They are charted according to the early period (before the first followup), at the 6-month followup, and at the last followup. The complications of the fractures are shown in Table 6 with the same chronologic sequences.

DISCUSSION

Most of the complications from treating peritrochanteric fractures occur with the unstable fractures. The fixation device that allows controlled collapse and fracture impaction gives the best clinical results. The Gamma nail attempts to combine the advantages of the sliding lag screw, which allows fracture impaction, and those of intra-medullary fixation. Biomechanically, the intramedullary device decreases the bending moment arm of the hip joint force on the implants by 25% to 30% when compared with the laterally fixed side plate. Biologically, the intramedullary fixation also allows the surgeon to fix the fractures with a closed procedure that minimizes the soft tissue dissection and fulfills the modern concept of fracture fixations.²¹ However, these attractive theoretic advantages are not reflected in many early clinical experiences.^3,9,12,23

The authors postulated that the causes for this observation are the geometric mismatch of the femoral shaft component to that of the proximal femur.¹⁸ The standard Gamma nail has 10 ° mediolateral angle and is 200 mm long. To insert the nail, a much larger volume of the femoral canal must be present to accommodate the nail of given diameter. This means that much of the cortical bone has to be reamed, thus weakening the osteoporotic bone in most patients.²² With the modified nail, nearly 60% of the fractures can be fixed with lesser degrees of reaming; in the later stages of this study, many of the fractures were fixed without reaming of the medullary canal. The decrease in the mediolateral curvature together with the shortened length of the nail also decreases the stress on the anterior cortex and the medical and lateral cortices. This effectively decreases the hoop stress inside the femoral shaft and may have contributed to a significant decrease in the intraoperative and postoperative diaphyseal fractures^24-26 in the proximal femurs. The other cause that contributes to the decrease in this complication is the modification of the operative technique with which the distal locking screws are applied. The understanding of the risk of creating fissures in the lateral cortex²⁰ during forceful use of the awl, which leads to stress riser and subsequently diaphyseal fracture, helps to modify the operative instrumentation and the operative technique.

One of the complications in fixing the peritrochanteric fractures is the superior cutout of the lag screw from the osteoporotic bone. Anatomic and biomechanical studies have shown that the superomedial quadrant of the femoral head is the weakest part for the implant.⁴ It also is the area where there is a concentration of the hip joint force.¹³ Thus, it is logical to avoid putting the screw into this region. With the design of the position of the lag screw 10 mm distal to the axis of the femoral head and neck and with the correct insertion of the femoral shaft component into the medullary canal, it can be ensured that the lag screw is inserted into the inferior ½ of the femoral head and neck, thus decreasing the incidence of superior cutout, as shown in this study (Table 6).

The analysis of the femoral component with the geometry of the proximal femur showed that anatomic match is observed in >94% of the cases (Fig 10). Cases from 1 of the trial centers showed a higher percentage of poor positioning of the nail. Additional analysis revealed that most of the fractures in the center were fixed in the varus position because of delays in operation. The average interval between injury and operation was 14.6 days, compared with 2.4 days in the other groups. The varus deformity prevented the proper positioning of the lag screw in the femoral head, which affected the insertion of the nail. This caused an excessive protrusion of the nail outside the greater trochanter, resulting in unnecessary irritation around the hip.

The overall intraoperative complication rate recorded in this study was approximately 7.7%, which was lower than the authors' previous report¹⁸(Table 3). Although most of the complications did not affect the outcome of the surgery, certain major complications occurred in the early stage of the trial (Fig 11). This could be explained by the operation being new to most of the surgeons when the trial started. As they gained more experience with the operative procedure, there was a rapid decrease in the intraoperative and postoperative complications.

When these results and complications are compared with the other series (Table 7), the current study shows better results. Although the available studies are not strictly comparable because the modified model with improved morphologic and biomechanical design was used, the differences reflect the preference for smaller implants⁹ and the improvement of clinical results and decline in complications as the surgeons become more experienced in the technique of Gamma nailing.^2,10

CONCLUSION

Improved clinical results using the Gamma nail, which has the combined advantages of a sliding lag screw and intramedullary femoral fixation, are shown in this multicenter trial. The modification of the implants according to anthropometric study results represents a scientific approach to a practical clinical problem. The modification provides an anatomic fit in the proximal femur and minimizes bone reaming during insertion. The revised lag screw position ensures that the lag screw be inserted into the inferior ½ of the femoral head and neck. The modifications have helped to decrease complications, and with better operative experience, the advantages of the Gamma nail are thoroughly expressed in the management of these common yet challenging fractures.

Fig 1: . The femoral shaft component of the (S) standard and (M) modified Gamma nails.

Fig 2: . Modified surgical technique for distal locking. Note the formation of a stable construct with the screw driver engaging the head of the proximal locking screw.

Fig 3: . Graph showing the distribution of patients according to different trial centers.

Fig 4: . Graph showing the age distribution of patients.

Fig 5: . Graph showing the anesthetic risk of the patients according to American Society of Anesthesiologists Scoring System.

Fig 6: . Graph showing the classification of fractures according to Evans classification.

Fig 7: . Graph showing the classification of fractures according to Singh's osteoporotic index.

Fig 8: . Graph showing the length of the lag screws used in the trial.

Fig 9A-B: . Graph showing the position of the lag screws in the femoral head on (A) frontal and (B) lateral views. Sup: superior; Inf: inferior; Med: Medial; Lat: lateral.

Fig 10: . Graph showing the analysis of the position of the femoral shaft component in the femoral canal.

Fig 11: . Graph showing the intraoperative complications charted according to the trial period.