Inferior Patellar Pole Avulsion Fractures: Osteosynthesis Compared with Pole Resection

Kastelec, Matej MD, MSc; Veselko, Matjaž MD, PhD

Journal of Bone & Joint Surgery - American Volume:
Scientific Articles
Abstract

Background: The ideal treatment for avulsion fractures of the inferior pole of the patella has not yet been identified. The options include (1) internal fixation of the pole fragment and (2) resection of the avulsed fragment and repair of the patellar ligament to the patella. We are not aware of any previous study in which the results of internal fixation have been compared with those of pole resection. The purpose of the present study was to compare the long-term results of internal fixation (with use of a basket plate) with those of pole resection.

Methods: We retrospectively studied two groups of patients who had had operative treatment of an avulsion fracture of the inferior patellar pole between 1990 and 1997. Fourteen patients had had internal fixation with a basket plate, and fourteen had had pole resection with patellar ligament repair. Eleven patients who had had internal fixation (Group A) and thirteen patients who had had pole resection (Group B) were followed for an average of 4.6 years. The final evaluation was based on the patellofemoral score, and the patesllar height was measured radiographically.

Results: The average patellofemoral score (maximum, 100 points) was 94.1 points in Group A and 81.2 points in Group B. Significant differences between the groups were noted with regard to knee pain, level of activity, and range of motion. Normal patellar height was found in ten of eleven patients in Group A and in three of thirteen patients in Group B. Patella baja was significantly associated with a poor functional outcome.

Conclusions: In patients who have sustained an avulsion fracture of the inferior patellar pole, the normal height of the patella can be maintained by preserving the patellar pole. In contrast with pole resection, which requires postoperative immobilization, internal fixation with a basket plate allows for immediate mobilization and early weight-bearing. The present study indicates that internal fixation with use of a basket plate can provide better clinical results.

Level of Evidence: Therapeutic study, Level III-2 (retrospective cohort study). See Instructions to Authors for a complete description of levels of evidence.

Author Information

1 Department of Traumatology, University Medical Centre Ljubljana, Zaloška 7, SI-1525 Ljubljana, Slovenia. E-mail address for M. Veselko: matjaz.veselko@kclj.si

Article Outline

In most fracture classification systems, avulsion fractures of the inferior patellar pole fall into a separate category1-5. Such fractures account for 9.3% to 22.4% of all patellar fractures that are treated surgically6.

An avulsion fracture of the distal patellar pole results from a blow to the flexed knee and the simultaneous forceful pull of the quadriceps muscle. The treatment of this type of fracture poses a special problem because of the structure of the injured patellar pole. An avulsion fracture with a single solid patellar pole fragment is best treated with fixation with use of a compression screw and cerclage wire7,8. Because of the trauma mechanism, however, the patellar pole is often comminuted. The treatment of choice in these cases often has been removal of the patellar pole and repair of the patellar ligament2,5,7,9,10. Some authors, however, have recommended preservation of the patellar pole by means of fixation with two cerclage wires3.

Internal fixation with a basket plate is an alternative method of treatment that, in contrast with other methods, allows for the preservation of the patella. The basket plate was designed for the treatment of comminuted distal patellar fractures by Smiljani in 1988 and was constructed in the Zagreb Department of Instrumentaria Research11. It has been tested mechanically in the Zagreb Faculty for Electrotechnology and Computing, and it has been tested clinically in the “Sestre Milosrdnice” Clinic in Zagreb, Croatia. Since 1990, it has been used in Croatia, Slovenia, Italy, Bosnia and Herzegovina, Macedonia, Yugoslavia, and other countries of the region. The device is available from Instrumentaria Zagreb, Rapska b.b., Cro-10000 Zagreb, Croatia (Ref. No. 60.338-01).

The basket plate has the shape of the inferior pole of the patella, which allows it to hold the comminuted patellar pole fragments in position. Fibers of the patellar ligament are pushed apart by four hooks on the plate that can be curved to fit the shape and size of the patella without damaging the articular surface (Fig. 1). The basket plate is fixed to the main patellar fragment with two parallel cancellous screws to provide interfragmentary compression. Another two screws, positioned obliquely, increase stability against distraction forces.

One of us (M.V.) and colleagues12 described a modification of the technique for the treatment of avulsion fractures of the inferior pole of the patella. To prevent slipping of the fragments between the plate hooks, which is likely to occur in association with avulsion fractures with multiple tiny fragments, absorbable interwoven sutures are placed through the patellar ligament, just beneath the fragments, and are used to tie the fragments into a bundle. The hooks are thrust into the patellar ligament beneath the suture line and the plate is then secured to the patella with screws (Fig. 1). Internal fixation with the basket plate is stable enough to allow for mobilization and weight-bearing on the first postoperative day. The patient is allowed to bear full weight on the affected extremity during level walking. For walking uphill or downhill, crutches should be used to prevent loading of the flexed knee joint for six weeks12.

The purpose of the present study was to compare the long-term results of internal fixation (with use of a basket plate) with those of pole resection, which is currently the most commonly used operative technique for the treatment of avulsion fractures of the inferior pole of the patella.

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Materials and Methods

We retrospectively reviewed the records of twenty-eight consecutive patients in whom an isolated avulsion fracture of the inferior patellar pole had been operatively treated at the Department of Traumatology at University Medical Centre Ljubljana, in Ljubljana, Slovenia, between 1990 and 1997. All fractures were displaced. Patients with fractures that extended beyond the pole and those with sleeve avulsions were not included. Fourteen patients were managed with basket plate fixation according to the technique described by one of us (M.V.) and colleagues12, and fourteen were managed with pole resection and transosseous suture fixation of the tendon to the patella according to the technique described by Saltzman et al.13.

Patients who were managed with the basket plate technique started passive motion exercises on the first postoperative day and were encouraged to perform active flexion exercises of the knee in the prone position. Active extension exercises were allowed after the third postoperative week. The patients were encouraged to start bearing weight on the second postoperative day during level walking, and full weight-bearing without limitation was encouraged from the sixth week on.

Patients who were managed with pole resection had immobilization of the involved knee for five to seven weeks (average, 6.5 weeks) postoperatively, during which time partial weight-bearing with crutches was allowed. After removal of the cast, patients began a rehabilitation program consisting of exercises designed to achieve a full range of motion, muscle training, and full weight-bearing.

The outcome of the procedure was assessed with use of the patellofemoral scoring system of Noyes et al.14, as adapted by Saltzman et al.13 to address problems of the patellofemoral joint. The evaluation involved the completion of a questionnaire (maximum score, 45 points), a clinical evaluation (maximum score, 43 points), and a radiographic analysis (maximum score, 12 points). The overall score was rated as excellent (90 to 100 points), good (80 to 89 points), fair (70 to 79 points), or poor (<70 points).

The patellar height was determined according to the criteria of Blackburne and Peel15. Lateral radiographs were made with the knee flexed by >30° to prevent laxity of the patellar ligament. With this method, the normal patellar height index is 0.80. The final result (according to the patellofemoral scoring system) for patients with patella baja was compared with that for patients with a normal patellar position, without regard to the type of treatment.

The statistical analysis of two independent samples was performed. The chi-square test was used to test the correlation between attributive variables (pain, swelling, function, and so on) in both samples. The Mann-Whitney U test was employed to analyze quantitative variables such as range of motion, muscle atrophy, and final outcome. The level of significance was set at p = 0.05.

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Results

The average age was 55.1 years (range, eleven to seventy-seven years) for the fourteen patients who were treated with internal fixation with a basket plate, compared with 50.5 years (range, twenty to seventy-two years) for the fourteen patients who were treated with pole resection. Of the fourteen fractures that were treated with a basket plate, eight resulted from a fall and six resulted from a car accident. Of the fourteen fractures that were treated with pole resection, seven resulted from a fall, five resulted from a car accident, and two resulted from sports-related trauma.

All patients were invited to return for a final follow-up evaluation. Two of the fourteen patients who had been managed with internal fixation had died and were not included in the study. In one other patient, internal fixation failed because of improper technique. This patient subsequently underwent another surgical procedure (pole resection) and was not included in the final evaluation. One of the fourteen patients who had been managed with pole resection had died and was not included in the study. All tendon repairs that were performed following pole resection healed.

The average time between the accident and the final evaluation was 4.5 years (range, 2.4 to 7.2 years) in the basket plate group and 4.7 years (range, 2.3 to 7.6 years) in the pole resection group. Eleven patients who had been treated with basket plate fixation (Group A) and thirteen patients who had been treated with pole resection (Group B) were evaluated at an average of 4.6 years.

At the time of the final follow-up, the average patellofemoral score was 94.1 points in Group A and 81.2 points in Group B (p = 0.013; t test) (Table I). In Group A, the score was excellent for ten patients and good for one. In Group B, the score was excellent for four patients, good for four, fair for three, and poor for two.

In Group A, seven patients were free of pain. Four patients, who had occasional pain after prolonged work or recreational activity, also complained of weather-related pain or said that they felt the joint “tighten.” The three patients who had participated in sports before the injury returned to the same sports after the injury. In Group B, three patients had no pain, five had pain after strenuous work or a change in the weather, three had pain after light work or recreational activity of moderate intensity, and two had constant pain. Of the three patients who had participated in recreational sports before the injury, one had to give up sports and two continued to participate in sports with limitation. The groups differed with regard to the score for knee pain (p = 0.025).

In Group A, the level of work activity remained unchanged for nine patients and was occasionally reduced for two. None of the patients had to change their job because of knee problems. In Group B, the level of work intensity remained unchanged for four patients, was occasionally reduced for eight, and was permanently limited for one. The latter patient was unable to return to work and had to apply for a disability pension. The groups differed with regard to the work intensity score (p = 0.011).

When the active range of motion of the involved knee was compared with that of the uninvolved knee, ten patients in Group A showed full flexion and one lacked 15° of full flexion. In Group B, five patients showed full flexion, seven had a flexion deficit of 0° to 15°, and one had a flexion deficit of >45°. The groups differed with regard to the active range of motion of the affected knee (p = 0.029).

The patellar height was assessed radiographically with use of the method of Blackburne and Peel15. Normal patellar height was found in ten of the eleven patients in Group A, compared with three of the thirteen patients in Group B. The patellar heights in Group A were distributed around the normal value; the average height was 0.77 in Group A, compared with 0.56 in Group B. This difference was significant (p = 0.013).

When the type of treatment was disregarded, the mean patellofemoral score was 81.9 points for all patients with patella baja and 94.7 points for all patients with a normal patellar position (p = 0.008).

Patients in whom the basket plate was left in place and those in whom the plate was subsequently removed showed similar results. The internal fixation devices were invariably well tolerated. The device was easily removed from seven patients after an average of six months.

Complications in the pole resection group included paresis of the peroneal nerve after immobilization in the plaster cast in one patient and infection of the wound in another patient. There were no complications in the internal fixation group.

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Discussion

We retrospectively studied twenty-eight consecutive patients who had had operative treatment of an isolated displaced avulsion fracture of the patellar pole. The present study did not include patients with comminuted fractures that extended beyond the patellar pole or patients with sleeve avulsions. The groups were comparable with regard to the number of patients, the age of the patients, and the type and cause of the injury. We compared two methods that are used in our department to treat such injuries, specifically, internal fixation with a basket plate and pole resection.

In our review of the literature, we found no studies that separately evaluated different methods of treatment of only avulsion fractures of the patellar pole and no studies that compared the results of internal fixation with those of patellar pole resection. Saltzman et al.13 evaluated the results of pole resection, but that study did not include only avulsion fractures but rather included all fractures for which partial patellectomy had been performed. Neumann et al.6 evaluated the long-term results for 135 patellar fractures that had been treated operatively between 1973 and 1989. Only fifteen of those fractures had been treated with partial patellectomy. Pelzl10 evaluated the results for sixty-four patients with comminuted fractures. Twenty-eight of the fractures had been treated with partial patellectomy, which was performed in all cases in which a solid proximal fragment formed at least two-thirds of the patellar size. Neither those studies nor other, similar studies evaluated avulsion fractures of the patellar pole separately1,2,6,7,10,13,16-19.

Our study group is small for statistical evaluation. The small size of our study group is related to the fact that these fractures are rare, accounting for only 9.3% to 22.4 % of all patellar fractures that are treated surgically6. We identified only twenty-eight cases of inferior pole avulsion fracture among sixty-three patients who had either partial patellectomy or internal fixation for a comminuted distal patellar fracture in our hospital over an eight-year period.

In the present study, 86% of the patients were available for a final evaluation. This rate is good compared with those in other reports in the literature, in which a final evaluation was possible for only 58% to 70% of patients with similar patellar fractures6,13,17.

The age of the patient and the type and cause of the injury had no effect on the final outcome. This observation corresponds with those in other reports on the outcome of partial patellectomy9,13. All fractures and all ligamentous repairs healed. Obvious signs of avascular necrosis of the inferior pole, a possible complication of the use of the plate, was not observed in any patient who was managed with plate fixation.

The purpose of the present study was to evaluate and to compare the long-term results of internal fixation and pole resection. For functional evaluation, we used the patellofemoral scoring system described by Saltzman et al.13 because it addresses the problems of the patellofemoral joint and is the only available system that provides a numerical evaluation of the functional results of treatment of patellar fractures.

We found a notable difference between the two treatment groups with regard to the final patellofemoral score (p = 0.013). In Group A, the mean score was 94.1 points and all of the results were either excellent or good. In Group B, the mean score was 81.2 points and five of thirteen results were fair or poor. The results in Group B correspond with those in the study by Saltzman et al.13, who reported 50% excellent, 27% good, and 23% fair and poor results. Significant differences between the groups were noted with regard to knee pain, level of activity, and range of motion.

At the time of the final follow-up assessment, a normal patellar height was established in ten patients in Group A and in only three patients in Group B (p = 0.013). These results also correspond with those in the study by Saltzman et al.13, who reported a low number of patients with normal patellar height after pole resection.

A possible explanation for the worse functional outcome for the patients who were managed with pole resection in the present study and in the study by Saltzman et al.13 could be the lower position of the patella, leading to shortening of the extensor mechanism. As a result of this shortening, compression forces in the patellofemoral joint increase, perhaps leading to cartilage damage3,18. In contrast, retaining the inferior patellar pole preserves the functional length of the extensor mechanism. A better functional outcome for patients with a preserved patellar position was also suggested when we compared the results for all patients who had patella baja with those for all patients who had a normal patellar position, without regard to the type of treatment. This comparison revealed that the patellofemoral score for patients with a normal patellar position was significantly higher than that for patients with patella baja.

Six weeks of immobilization in a plaster cast following patellar pole resection is known to have harmful effects on the involved knee joint and muscles20. Immediate postoperative mobilization and early full weight-bearing on the affected joint are two important advantages conferred by basket plate osteosynthesis in addition to the advantages of preservation of the functional length of the extensor mechanism and the normal height of the patella.

Figures 2 and 3 show radiographs of the knees of two patients of the same age, made 2.5 years after the operative treatment of an avulsion fracture of the inferior patellar pole. The first patient was treated with inferior pole resection (Fig. 2), and the other patient was treated with internal fixation with use of a basket plate (Fig. 3). A comparison of the operatively treated knees with the contralateral knees shows the difference in the patellar height and the extent of degenerative changes involving the patellofemoral joint associated with these two forms of treatment.

The study groups in the present study were small, and differences between the groups should be judged cautiously. Nevertheless, the results of the present study demonstrate that the principle of retaining the fragments and maintaining normal patellar height is beneficial and that stable fixation that permits immediate mobilization of the joint and early full weight-bearing can contribute to a better functional outcome in the treatment of avulsion fractures of the inferior patellar pole.

The authors did not receive grants or outside funding in support of their research or preparation of this manuscript. They did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

Investigation performed at the Department of Traumatology, University Medical Centre Ljubljana, Ljubljana, Slovenia

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