Ankle fusion for bone loss around the ankle joint using the Ilizarov technique

Midterm Results after Tibiotalar or Tibiotalocalcaneal Fusion Using an Ilizarov External Fixator

Background

Ankle fusion is considered a treatment of choice for end-stage ankle arthritis when a total ankle replacement procedure is not indicated. However, the potential risk of secondary arthritis in the adjacent joint after ankle fusion raises arguments on whether preserving the adjacent joint during an isolated tibiotalar (TT) fusion brings about any future benefits with regard to pain and gait discomfort. In this study, we intended to present midterm results following TT or tibiotalocalcaneal (TTC) fusion using an Ilizarov external fixator and to investigate whether spontaneous fusion occurred in the subtalar or midtarsal joint.

Methods

This is a retrospective observational study. Medical records of patients who underwent TT or TTC fusion using an Ilizarov external fixator for substantial bone defects around the ankle joint between 1994 and 2018 were manually searched. Forty-one patients were included and the status of the joints adjacent to the fusion site was evaluated in radiographic examinations.

Results

Of the 34 patients who underwent TT fusion, 30 patients (88.3%) had a spontaneous fusion in the adjacent joints. Specifically, 11 patients (29.4%) had subtalar joint fusion and 19 patients (55.9%) had both midtarsal joint and subtalar joint fusion. In TTC fusion, the midtarsal joint was spontaneously fused in all 7 patients.

Conclusions

In this study, we observed spontaneous adjacent joint fusion following TT or TTC fusion using an Ilizarov external fixator for substantial bone defects around the ankle joint. Although a careful approach should be made since patients treated in this study may not represent typical candidates that need primary joint-sacrificing procedures, we believe that this study may draw attention from surgeons concerned about the fate of the adjacent joint status after TT or TTC fusion.

Comparative results of arthroscopic ankle arthrodesis vs. open arthrodesis in patients with diabetes-associated Charcot Neuro-Arthropathy

BACKGROUND

Several studies demonstrated a considerable complication rate for open ankle or TTC arthrodesis in patients with diabetes, revision surgery and ulceration. Extensive approaches in combination with multimorbide patients have been suggested as the rationale behind the increased complication rate.

METHODS

Single-centre, prospective case-control study compared arthroscopic vs. open ankle arthrodesis in patients with Charcot Neuro-Arthropathy of the foot. 18 patients with septic Charcot Neuro-Arthropathy Sanders III-IV received an arthroscopic ankle arthrodesis with TSF (Taylor Spatial Frame®) fixation combined with different additional procedures required for infect treatment and hindfoot realignment. The ankle arthrodesis was required for the realignment of the hindfoot in Sanders IV patients, arthritis or in case of infection. 12 patients were treated with open ankle arthrodesis and TSF fixation combined with various additional procedures.

RESULTS

A significant improvement has been shown in radiological data in both groups. A significant lower complication rate has been registered in arthroscopic group. A significant correlation was seen between major complications and therapeutic anticoagulation as well as smoking.

CONCLUSION

In high-risk patients with diabetes and plantar ulceration excellent results could be demonstrated in arthroscopically performed ankle arthrodesis with midfoot osteotomy using TSF as fixation devise.

Complex Ankle Fusion With Circular Frames: Factors Influencing Outcomes, Complications, and Patient Satisfaction

BACKGROUND

Circular frames for ankle fusion are reserved for complex clinical scenarios. The literature is heterogenous and conflicting. We aim to present the indications and outcomes of this procedure.

METHODS

A retrospective cohort study based on a prospective database of frame surgeries performed in a tertiary institution. Inclusion criteria were patients undergoing complex ankle fusion with circular frames between 2005 and 2020, with a minimum 12-month follow-up. Data were collected on patient demographics, surgical indications, comorbidities, surgical procedures, external fixator time (EFT), length of stay (LOS), radiologic and clinical outcomes, and adverse events. Factors influencing radiologic and clinical outcomes were analyzed.

RESULTS

47 patients were included, with a median follow-up of 30 months (interquartile range [IQR] 20-40). The median age at time of surgery was 63.5 years (IQR 58-71). Patients had a median of 2 previous surgeries (IQR 1-3). The median LOS was 8.5 days, and median EFT was 237 days (IQR 166-280). Simultaneous limb lengthening (median 3.3 cm, IQR 1.9-3.5) was performed in 11 patients, increasing the EFT by a mean of 4 months. Primary and final union rates were 91.5% and 95.7%, respectively. At last follow-up, ASAMI bone scores were excellent or good in 87.2%. ASAMI functional scores were good in 79.1%. Patient satisfaction was 83.7%. In addition, 97.7% of patients experienced adverse events, most commonly pin-site related, with major complications in 30.2% and reoperations in 60.5%. There were 3 amputations. Adverse events were associated with increased age, poor soft tissue condition, severe deformities, subtalar fusions, peripheral neuropathy, peripheral vascular disease, and prolonged EFT.

CONCLUSION

Complex ankle fusion using circular frames can achieve good outcomes, however time in frame may be prolonged with a high rate of adverse events. Identified risk factors for poorer outcomes should be considered in patient counselling and prognostication.

LEVEL OF EVIDENCE

Level III, prognostic.

Increased Arthrodesis Rates in Charcot Neuroarthropathy Utilizing Distal Tibial Distraction Osteogenesis Principles

Charcot neuroarthropathy of the hindfoot and ankle poses substantial challenges due to deformity, segmental bone loss, chronic infection, and difficulty with bracing. Hindfoot or ankle arthrodesis is often employed at high rates of complications and nonunion. This study reports 15 consecutive patients with Charcot neuroarthropathy who underwent tibiotalocalcaneal or tibiocalcaneal fusion with simultaneous distal tibial distraction osteogenesis with a mean follow-up period of 20.2 ± 5.66 months. Arthrodesis rate was 93.3% (14 patients) with mean time to fusion of 4.75 ± 3.4 months. One hypertrophic nonunion occurred at the arthrodesis site. Complete consolidation of 4 cortices was achieved at the distraction site in 93.3% of patients (14 patients) with a mean duration to consolidation of 9.8 ± 3.3 months. One patient experienced hypertrophic nonunion at the regeneration site. The authors report a technique to enhance arthrodesis rates in Charcot neuroarthropathy by combining distal tibial distraction osteogenesis with simultaneous tibiotalocalcaneal or tibiocalcaneal arthrodesis for hindfoot fusion and salvage. Distraction osteogenesis supports enhanced vascularity to the arthrodesis site.Level of Clinical Evidence: Level 4.

Simultaneous Limb Lengthening With Ankle Fusion Using an Internal Lengthening Nail

We reviewed 18 limbs in 17 patients who underwent ankle fusion with simultaneous tibial lengthening with a magnetic internal lengthening nail. All patients had preoperative limb length discrepancy (LLD) (mean 4.9 cm (2.6-7.6 cm)) with ankle deformity. The ankle was fused from medial or lateral approaches using screws/plate constructs placed adjacent to the retrograde Precise nail. Lengthening was carried out by a distal 1/3 tibial osteotomy. Clinical and radiographic measures were performed after a mean follow-up of 20 months (12-37 months). The mean amount of lengthening performed was 4 cm (1.8-7.2 cm). The final mean LLD was 1 cm (0.7-1.1 cm), which was statistically significant (p<0.01) as compared to preoperative. The foot was plantigrade in all cases. The mean foot rotation was 10° (5-15°) external, relative to the knee. At final follow-up all patients reported minimal to no pain, and all claimed to be walking more functionally than before surgery. Ankle fusion and limb lengthening was achieved in all cases. Combining both treatments by using an internal lengthening nail was very effective and avoided leaving patients with a dysfunctional LLD or of having a separate limb lengthening procedure. This is the first report of such a combined treatment of ankle fusion with internal tibial lengthening nail.

Tibiocalcaneal arthrodesis using the Ilizarov fixator in compromised hosts: an analysis of 19 patients

INTRODUCTION

Salvage of joint destruction of the tibiotalar and subtalar joint with necrosis or infection of the talus in compromised hosts is a challenging problem. In these cases, tibiocalcaneal arthrodesis using the Ilizarov external fixator represents a possible alternative to amputation. This retrospective study presents the results and complications of this salvage procedure.

MATERIALS AND METHODS

Between 2005 and 2015, 19 patients were treated with tibiocalcaneal arthrodesis using the Ilizarov external fixator. Ten patients received tibiocalcaneal arthrodesis due to an acute or chronic infection with joint destruction. The other nine patients presented posttraumatic necrosis of the talus or Charcot arthropathy. In addition to demographic data, the time spent in the fixator, the major and minor complications and the endpoint of the consolidation were evaluated retrospectively. Furthermore, clinical outcomes were measured using the modified American Orthopedic Foot and Ankle Society (AOFAS) score.

RESULTS

The average time spent in the fixator was 22 (range 14-34) weeks. The average follow-up in 17 patients was 116 (range 4-542) weeks. Two patients were lost to follow-up. Complete osseous consolidation was achieved in 14 out of 19 patients. One patient presented partial consolidation, and in four patients, pseudarthrosis could be detected. The mean modified AOFAS score at the final follow-up was 53 out of 86 possible points.

CONCLUSION

Tibiocalcaneal arthrodesis using the Ilizarov fixator is a possible salvage procedure even in compromised hosts. However, the healing rates are below the rates reported in the literature for tibiotalar arthrodesis in comparable clinical situations.

Simultaneous septic arthrodesis of the tibiotalar and subtalar joints with the Ilizarov external fixator-an analysis of 13 patients

Purpose

Treatment of joint destruction of the tibiotalar and subtalar joints caused by acute or chronic infections in compromised hosts is a challenging problem. In these cases, simultaneous septic arthrodesis with the use of the Ilizarov external fixator represents a possible alternative to amputation. This case series presents the results and complications of patients with acute or chronic infection of the tibiotalar and subtalar joints.

Methods

Between 2005 and 2015, 13 patients with acute or chronic infections were treated by simultaneous single-stage debridement/arthrodesis of the tibiotalar and subtalar joints. In seven patients, there was a florid infection with fistula formation and soft tissue defects, and in six patients, there was chronic osteomyelitis with closed soft tissue. In addition to the demographic data, the time spent in the fixator, the major and minor complications and the endpoint of consolidation were reviewed.

Results

The mean time spent in the fixator was 18 (min 15, max 26) weeks. The mean follow-up time for nine patients was 100 (min 3, max 341) weeks. Complete osseous consolidation of both the tibiotalar and subtalar joints was achieved in 10 patients (77%). In three (23%) patients, there was complete consolidation of one of the joints and partial consolidation of the other joint.

Conclusion

The Ilizarov external fixator allows for simultaneous arthrodesis of the tibiotalar and subtalar joints in septic joint destruction. However, the healing rates are below the rates reported in the literature for isolated tibiotalar or tibiocalcaneal arthrodesis in comparable clinical situations.

External versus internal fixation for arthrodesis of chronic ankle joint infections - A comparative retrospective study

BACKGROUND

Arthrodesis of the ankle is a salvage procedure in case of chronic ankle joint infection. External fixation still is the gold standard. We compared the outcome of external fixator versus intramedullary nailing for arthrodesis of the infected ankle joint.

METHODS

All patients with ankle joint infection who received arthrodesis with either external fixator or intramedullary nail between 08/2009 and 09/2017 were retrospectively analyzed. Endpoints were the successful control of infection, osseous fusion, and mobilization with full weightbearing.

RESULTS

Seventy-one patients were included. Nineteen patients (27%) suffered reinfection. Patients with intramedullary nailing showed significantly fewer reinfections (p=0.019), achieved full weightbearing significantly more often (p=0.042) and faster and developed significantly fewer complications (p<0.001). Forty-three patients showed bone fusion without significant differences between the groups.

CONCLUSIONS

Ankle arthrodesis with intramedullary nailing appears to be a successful alternative to the established procedure of external fixation in cases of chronic ankle joint infection.

Staged distraction osteogenesis followed by arthrodesis using internal fixation as a form of surgical treatment for complex conditions of the ankle

Aims

The aim of this study was to describe the technique of distraction osteogenesis followed by arthrodesis using internal fixation to manage complex conditions of the ankle, and to present the results of this technique.

Patients and Methods

Between 2008 and 2014, distraction osteogenesis followed by arthrodesis using internal fixation was performed in 12 patients with complex conditions of the ankle due to trauma or infection. There were eight men and four women: their mean age was 35 years (23 to 51) at the time of surgery. Bone healing and functional recovery were evaluated according to the criteria described by Paley. Function was assessed using the ankle-hindfoot scale of the American Orthopedic Foot and Ankle Society (AOFAS).

Results

A solid fusion of the ankle and eradication of infection was achieved in all patients. A mean lengthening of 6.1 cm (2.5 to 14) was achieved at a mean follow-up of 25.2 months (14 to 37). The mean external fixation index (EFI) was 42 days/cm (33.3 to 58). The function was judged to be excellent in six patients and good in six patients. Bone results were graded as excellent in ten patients and good in two patients. The mean AOFAS score was 37.3 (5 to 77) preoperatively and 75.3 (61 to 82) at the final follow-up. Minor complications, which were treated conservatively, included pain, pin-tract infection, loosening of wires, and midfoot stiffness. Major complications, which were treated surgically included grade V pin-tract infection with inflammation and osteolysis, poor consolidation of the regenerate bone, and soft-tissue invagination. The reoperations required to treat the major complications included the exchange of pins and wires, bone grafting and invagination split surgery.

Conclusion

The technique of distraction osteogenesis followed by arthrodesis using internal fixation is an effective form of treatment for the management of complex conditions of the ankle. It offers a high rate of union, an opportunity to remove the frame early, and a reduced EFI without infection or wound dehiscence. Cite this article: Bone Joint J 2018;100-B:755–60.

Early results of a novel technique: Hindfoot fusion in talus osteonecrosis prior to ankle arthroplasty: A case series

BACKGROUND

The purpose of this study was to evaluate the clinical outcome of a two staged approach of subtalar arthrodesis followed by TAR for patients with ankle arthritis and AVN talus.

METHODS

Out of total 210 TARs performed at our institute; 7 patients underwent a two staged procedure between 2006 and 2010. All patients had over 3 years of follow up (except one). The clinical results were assessed using AOFAS, WOMAC, SF-36 and patient satisfaction scores.

RESULTS

The mean follow up was 3 years. There was significant improvement in AOFAS and WOMAC (pain and stiffness) from pre-op to 3 years post-op (P<0.05). SF 36 scores improved from pre-op to 3 years post-op for 6/8 domains. 5 patients were satisfied at 3 years for overall surgical outcomes, 4 were satisfied with pain relief. Radiological signs of talar subsidence were noted in 2 patients at year 1. This did not progress at 3 years and did not deteriorate clinical outcome.

CONCLUSION

We recommend our two staged approach to deal with this difficult clinical problem. We believe this approach is safe for TAR surgery where talar vascularity and bone quality is questionable leading to reduced talar subsidence, ischaemic pain and improvement in longevity of TAR.

LEVEL OF EVIDENCE

Evidence IV (Retrospective case series).

Total and subtotal amputation of lower limbs treated by acute shortening, revascularization and early limb lengthening with ilizarov ring fixation - a retrospective study

We present the results of 15 patients who sustained total or subtotal traumatic amputation of the lower limbs who were treated by acute limb shortening and stabilisation with external fixator, revascularization and early lengthening with Ilizarov ring fixator. The mean age of the patients was 28 years [5-38]. There were three females and 12 males. The mean Mangled Extremity Severity Score was 8.5 [range 6-11]. The mean amount of shortening done was 6.9cm [range 3-12.5] to enable revascularization and soft tissue repair. Three cases had to be amputated early because of failure of vascular repair. In the remaining 12 patients who were followed up the mean interval between revascularization and application of Ilizarov ring fixator was 4.7 weeks [range 3-10]. The mean follow up was 6.5 years [3-16 years]. Union occurred in all patients. Ten of the 12 patients returned to work and residual shortening was present in two cases. We conclude that whenever possible lower limb salvage should be undertaken.

An Alumina Ceramic Total Talar Prosthesis for Osteonecrosis of the Talus

BACKGROUND

Treatment of osteonecrosis of the talus is challenging. Total talar replacement has the potential to restore the function of the ankle joint without an associated leg-length discrepancy. The purpose of the present study was to investigate postoperative function and pain after total talar replacement in patients with osteonecrosis of the talus.

METHODS

Fifty-five ankles in fifty-one consecutive patients with osteonecrosis of the talus who were treated with a total talar replacement from 2005 to 2012 were included in the investigation. Scores according to the Japanese Society for Surgery of the Foot (JSSF) ankle-hindfoot scale and the Ankle Osteoarthritis Scale (AOS) were assessed before surgery and at the final follow-up evaluation.

RESULTS

According to the JSSF ankle-hindfoot scale, the score for pain improved from a mean (and standard deviation) of 15 ± 9.4 points (range, 0 to 20 points) to 34 ± 5.6 points (range, 20 to 40 points); the score for function, from 21.2 ± 9.7 points (range, 4 to 38 points) to 45.1 ± 4.0 points (range, 37 to 50 points); the score for alignment, from 6.0 ± 2.8 points (range, 5 to 10 points) to 9.8 ± 0.9 points (range, 5 to 10 points); and the total score, from 43.1 ± 17.0 points (range, 11 to 68 points) to 89.4 ± 8.4 points (range, 76 to 100 points). According to the AOS scale, the score for "pain at its worst" improved from a mean of 6.1 ± 3.3 points (range, 0 to 9.9 points) to 2.0 ± 1.7 points (range, 0 to 6.3 points).

CONCLUSIONS

Prosthetic talar replacement is a useful procedure for patients with osteonecrosis of the talus as it maintains ankle function.

Strategies for managing bone defects of the lower extremity

Management of posttraumatic segmental bone loss as a result of severe open injuries of the lower extremity, high-energy closed injuries, and following failed initial treatment of complex fractures that develop pseudarthrosis continues to challenge reconstructive surgeons. There are numerous strategies for dealing with such injuries but the outcome is unpredictable. The procedure is rarely only one stage and complications frequently arise. In most cases the reconstruction process is long and difficult and amputation must be part of the decision-making process. All traditional treatment strategies have advantages and major drawbacks. To overcome some limitations, biologic treatments have been developed based on specific pathways of bone physiology and healing.

Ankle arthrodesis fusion rates for mesenchymal stem cell bone allograft versus proximal tibia autograft

Ankle arthrodesis is commonly used in the treatment of ankle arthritis. The present study compared mesenchymal stem cell (MSC) bone allografts and proximal tibia autografts as adjuncts in performing ankle arthrodesis. A total of 109 consecutive ankle fusions performed from 2002 to 2008 were evaluated retrospectively. Of the 109 fusions, 24 were excluded from the present study, leaving 85 patients who had undergone ankle arthrodesis. Of the 85 patients, 41 had received a proximal tibia autograft and 44, an MSC bone allograft. These 2 groups were reviewed and compared retrospectively at least 2 years postoperatively for the overall fusion rate, interval to radiographic fusion, and interval to clinical fusion. A modified and adjusted American College of Foot and Ankle Surgeons ankle scale was used to measure patient satisfaction. The overall fusion rate was 84.1% in the MSC bone allograft group and 95.1% in the proximal tibia autograft group (p = .158). The corresponding mean intervals to radiographic fusion were 13.0 ± 2.5 weeks and 11.3 ± 2.8 weeks (p ≤ .001). The interval to clinical fusion was 13.1 ± 2.1 weeks and 11.0 ± 1.5 weeks (p ≤ .001) in the MSC bone allograft and proximal tibia autograft group, respectively. No statistically significant difference was found in the fusion rates between the MSC bone allograft and proximal tibia autograft groups. Also, no statistically significant difference was found between the preoperative and postoperative scores using a modified and adjusted American College of Foot and Ankle Surgeons ankle scale between the 2 groups (p = .41 and p = .44, respectively). A statistically significant delay to radiographic and clinical fusion was present in the MSC bone allograft group compared with the proximal tibia autograft group; however, no difference was found in patient satisfaction.

The use of a ceramic talar body prosthesis in patients with aseptic necrosis of the talus

The purpose of this study was to evaluate the clinical results of a newly designed prosthesis to replace the body of the talus in patients with aseptic necrosis. Between 1999 and 2006, 22 tali in 22 patients were replaced with a ceramic prosthesis. A total of eight patients were treated with the first-generation prosthesis, incorporating a peg to fix into the retained neck and head of the talus, and the remaining 14 were treated with the second-generation prosthesis, which does not have the peg. The clinical results were assessed by the American Orthopaedic Foot and Ankle Society ankle/hindfoot scale. The mean follow-up was 98 months (18 to 174). The clinical results of the first-generation prostheses were excellent in three patients, good in one, fair in three and poor in one. There were, however, radiological signs of loosening, prompting a change in design. The clinical results of the second-generation prostheses were excellent in three patients, good in five, fair in four and poor in two, with more favourable radiological appearances. Revision was required using a total talar implant in four patients, two in each group. Although the second-generation prosthesis produced better results, we cannot recommend the use of a talar body prosthesis. We now recommend the use of a total talar implant in these patients.

Outcome of arthrodesis of the hindfoot as a salvage procedure for complex ankle pathology using the Ilizarov technique

Achieving arthrodesis of the ankle can be difficult in the presence of infection, deformity, poor soft tissues and bone loss. We present a series of 48 patients with complex ankle pathology, treated with the Ilizarov technique. Infection was present in 30 patients and 30 had significant deformity before surgery. Outcome was assessed clinically and with patient-reported outcome measures (Modified American Orthopaedic Foot and Ankle Society (MAOFAS) scale and the Short-Form (SF-36)).

Arthrodesis was achieved in 40 patients with the Ilizarov technique alone and in six further patients with additional surgery. Infection was eradicated in all patients at a mean follow-up of 46.6 months (13 to 162). Successful arthrodesis was less likely in those with comorbidities and in tibiocalcaneal fusion compared with tibiotalar fusion.

These patients had poor general health scores compared with the normal population before surgery. The mean MAOFAS score improved significantly from 24.3 (0 to 90) pre-operatively to 56.2 (30 to 90) post-operatively, but there was only a modest improvement in general health; the mean SF-36 improved from 44.8 (19 to 66) to 50.1 (21 to 76). There was a major benefit in terms of pain relief.

Arthrodesis using the Ilizarov technique is an effective treatment for complex ankle pathology, with good clinical outcomes and eradication of infection. However, even after successful arthrodesis general health scores remain limited.

Cite this article: Bone Joint J 2013;95-B:371–7.

Traumatic loss of talus: a rare injury

BACKGROUND

Traumatic loss of talus during a compound injury of ankle is an unusual injury.

OBJECTIVE

We report a 55 years old woman who sustained an open ankle injury with complete extrusion of talus and loss at the injury site.

METHOD

A tricortical bone graft was obtained from iliac crest and talar dimensions carved with 5 cm length and 3 cm height given by buttressing fibular graft between them. These grafts are made in the shape of talus by fixing them together with cortical screw and binding them together with Ethibond No. 5. By anterior approach ankle was opened and talar graft was placed in between the raw surfaces of tibia and calcaneus to facilitate ankle arthrodesis.

RESULT

Patient had solid fusion at the ankle joint after 4 months with no pain on walking.

CONCLUSION

The definitive treatment of this serious lower extremity injury remains controversial we have attempted this novel way of treatment as the patient was unable to afford talar prosthesis and facilities of allogenic bone grafts were not there.

Complex ankle arthrodesis using the Ilizarov method yields high rate of fusion

BACKGROUND

Ankle arthrodesis may be achieved using the Ilizarov method. Comorbidities, such as diabetes, Charcot neuroarthropathy, osteomyelitis, leg length discrepancy, and smoking, can make an ankle fusion complex and may be associated with lower rates of healing.

QUESTIONS/PURPOSES

We asked if (1) smoking and other comorbidities led to lower fusion rates, (2) time wearing the frame affected outcome, and (3) simultaneous tibial lengthening improved fusion rates.

METHODS

We retrospectively studied 101 patients who underwent complex ankle fusion using the Ilizarov technique. The median time wearing the frame was 25 weeks (range, 10-65 weeks). Twenty-four patients had simultaneous tibial lengthening. The minimum followup for 91 of the 101 patients was 27 months (median, 65 months; range, 27-134 months).

RESULTS

Fusion was achieved in 76 of 91 patients. Smoking was associated with a 54% rate of nonunion. Fifteen of 19 patients with Charcot neuroarthropathy achieved union but had a high rate of subsequent subtalar joint failure. Time wearing the frame did not affect union rates. Tibial lengthening did not improve ankle fusion rates.

CONCLUSION

Smokers should be warned of the high risk of nonunion and we recommend they quit smoking. We also recommend surgeons recognize the higher nonunion rate in patients with Charcot neuroarthropathy. We believe tibial lengthening should not be performed to enhance healing at the fusion site.

LEVEL OF EVIDENCE

Level IV, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.