Highlights
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The egg shell procedure provides an innovative approach to hip replacement for patients with bone tumors.
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This technique is associated with improved joint mobility in patients with bone tumors.
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Good quality of life observed in patients with bone tumors treated using the egg shell procedure.
Keywords: Eggshell procedure, Proximal femoral replacement, Femoral tumor, Hip dislocation, Limb function
Abstract
Purpose
Proximal femoral replacement (PFR) for oncology patients is gaining interest as a limb salvage operation due to its obvious advantages. However, almost all hip replacement surgeries including PFR, are faced with the challenge of how to reconstruct the functional musculature in an optimal way. To address the challenge, we have developed an innovative eggshell procedure and through this study we aim to investigate the specific efficacy of the procedure.
Methods
A total of 44 tumor patients with PFR surgery were incorporated into the study, including 12 who underwent the eggshell procedure and 32 who did not. General characteristics, short-term indicators, long-term indicators and complication outcomes were compared successively between the two groups of patients.
Results
No significant differences were identified in general characteristics between the two groups. Overall, in terms of both short-term and long-term indicators, the patients with eggshell procedure performed significantly superior to the patients without it. Moreover, the eggshell procedure significantly reduced the incidence of associated complications, including prosthesis dislocation and hip pain.
Conclusions
Our eggshell procedure is convenient and accessible. On the one hand, it can reduce surgical side injuries without adding additional complications, and on the other it allows to improve joint mobility and life quality while diminishing the incidence of prosthesis dislocation and hip pain. Despite it may still remain limitations, we have reasons to believe that this procedure can be further promoted and applied.
1. Introduction
The proximal femur is a common site of bone tumor growth, which frequently leads to prolonged unbearable pain and even pathological fractures that can have a serious negative impact on the patient's overall quality of life [1]. Accordingly, proximal femoral replacement (PFR) by prosthesis after resection of the tumor segment bone has become emerging and is gaining increasing attention as a salvage reconstructive procedure [2]. Compared to traditional amputation, PFR preserves the limb appearance and is the treatment option with most promise of restoring function to the affected limb [3]. More notably, if the condition of acetabulum is adequate, PFR as a hemiarthroplasty is generally a more desirable choice for patients than total hip replacement (THR) [4]. Nevertheless, with the current PFR technique, postoperative instability of the hip abductor (represented by the gluteus medius) and external rotator (represented by the piriformis) muscles may result in series of severe consequences such as prosthesis dislocation and restricted motion [5]. It still remains an urgent problem to reduce the incidence of postoperative complications and to improve the joint mobility so as to guarantee the postoperative patient's quality of life.
The term “eggshell procedure” originated in spinal surgery, In the 1980 s, Heinig developed a technique to decompress spinal fractures by hollowing out the vertebral body through the pedicle and then ramming the posteriorly convex fracture into the emptied vertebra [6]. It is termed “eggshell procedure” as the cancellous bone of the vertebral body is completely removed and only a thin shell of cortical bone remains, which is similar in shape to an eggshell. The emergence of this procedure in spinal surgery is considered to be highly creative and imaginative. Instead, we migrated the “eggshell procedure” to femoral replacement surgery for oncology patients as an innovative technique that brings fresh significance to the term.
The whole process of our eggshell procedure is convenient and accessible. We preserved the greater trochanter and debrided the cancellous bone to conserve the cortical bone prior to resection of the femoral tumor segment, and then attached the greater trochanter cortex to the artificial prosthesis to complete the reconstruction after satisfactory installation of the prosthesis. The hollowed-out greater trochanter not only resembles an eggshell, but more crucially, its vital anatomical structure is retained through which it functions accordingly. Widely accepted, the abductor muscles of the hip joint include the gluteus medius, gluteus minimus and tensor fascia lata, and the external rotator muscles of the hip joint include the piriformis, superior gemellus, inferior gemellus, obturator internus, obturator externus and quadratus femoris [7]. Since all of the above muscles except the tensor fascia lata have their insertion on the greater trochanter, theoretically the retention of the greater trochanter due to eggshell procedure can substantially improve the ability of hip abduction and external rotation, prevent the occurrence of complications like dislocation, and potentially provide significant assistance in the functional recovery of the affected limb. In this context, we implemented a retrospective cohort study in an attempt to confirm and evaluate the specific clinical value of this novel technology.
2. Methods
2.1. Study design and participants
In our hospital database, we reviewed the patients who received PFR after resection of femoral tumor segment from January 2017 to January 2022. Among them, in order to ensure the consistency of the included samples, we excluded the patients with primary femoral sarcoma, and only patients with cancer metastasis to the femur were selected as subjects. Eventually, a total of 44 patients were incorporated into the study, including 12 with eggshell procedure and 32 without it.
Preoperatively, for patients with indications for the eggshell procedure (theoretically requiring tumor invasion below the lesser trochanter due to the necessity of intercepting an adequate greater trochanter, and at least 12 cm from the distal femur to ensure the stability of the prosthesis inserted into the distal femur) (Fig. 1A), the surgeon would recommend this technique. Meanwhile, these patients were notified that the application of eggshell procedure could not guarantee a definite advantage and could lead to increased blood loss, prolonged operation time or other unpredictable accidents. The decision was ultimately made by the patient after a joint discussion with surgeon. Our study was in line with the Declaration of Helsinki and was approved by our hospital ethics committee. Informed consent was gained from patients and their families, and all patient data involved in the study were acquired from our medical records.
Fig. 1.
A-C. Schematic diagram of eggshell procedure. (A) Theoretical application scope of eggshell procedure. (B) Anterior view of the greater trochanter osteotomy. (C) Dorsal view of the greater trochanter osteotomy.
2.2. Surgical treatment
All operations were performed by two senior orthopedic surgeons. All were conducted using a lateral approach to the hip (Watson-Jones approach), and the proximal femur and greater trochanter were exposed after separating the superficial tissues.
Patients who underwent the eggshell procedure retained approximately 1.5 cm of normal bone distal to the apex of the greater trochanter, so as to preserve as much as possible the insertion of hip abductor muscle group (represented by the gluteus medius) and external rotator muscle group (represented by the piriformis) on the greater trochanter (Fig. 1B-C). After designing the osteotomy plane under intraoperative fluoroscopy (Fig. 2A), an oblique osteotomy was performed along the greater trochanter with a pendulum saw (Fig. 2B). The reserved greater trochanter was then turned proximally after excavating the cancellous bone and keeping the cortical bone (Fig. 2C) to reveal the operative field for subsequent enlarged resection of the tumor segment bone (Fig. 2D). Furthermore, once the prosthesis was satisfactorily mounted, we covered and fixed the greater trochanter cortex to the lateral side of the proximal femoral prosthesis using titanium cables (tough non-absorbable sutures could serve as a second option if titanium cables were not available), with the aim of broadly restoring the primary anatomy of the greater trochanter and thereby reconstructing the functional musculature of the hip joint (Fig. 2E). The postoperative review x-ray was demonstrated in Fig. 2F.
Fig. 2.
A-F. Practical application of eggshell procedure. (A) The location of greater trochanter osteotomy determined under intraoperative fluoroscopy. (B) Oblique osteotomy of greater trochanter before resection of tumor segment bone. (C) The greater trochanter cortex shaped like an eggshell after hollowing out the cancellous bone. (D) Loss of the greater trochanter as observed after resection of the femoral tumor segment. (E) Reconstruction of the greater trochanter on the prosthesis during surgery. (F) Postoperative review of the prosthesis and the retained greater trochanter.
In patients without eggshell procedure, the severed abductor and external rotator muscle groups were reattached to the lateral aspect of the proximal femoral prosthesis using nonabsorbable sutures after the enlarged resection of the tumor segment bone and the installation of the prosthesis. Beyond that no additional reconstruction techniques were taken. All implants were LiDaKang (LDK Co, Beijing, China) proximal femoral prostheses with a bipolar femoral head component.
2.3. Rehabilitation and follow-up
All postoperative patients wore an abduction brace and uniformly underwent a 12-week, multi-stage rehabilitation program for lower extremity function. The first phase of the program (1–7 days postoperatively) was designed to provide instructional therapy for potential acute complications during hospitalization and involved a series of rehabilitation interventions including ankle pump exercise, cold therapy, affected limb elevation, and isometric contraction practice of the lower extremity muscles. The second and third stage rehabilitation plan of patients was carried out under the supervision and guidance of the physiotherapists outside the hospital. The second phase of the program (2–8 weeks postoperatively) aimed to guide the rehabilitation treatment for restricted joint movement, decreased muscle strength and active pain observed during the follow-up process. The third phase of the program (8–12 weeks postoperatively) mainly focused on the rehabilitation issues such as balance disorder, gait disturbance, and reduced proprioception identified in the functional evaluation.
Patients were advised to visit the outpatient clinic for follow-up at 3-month intervals after surgery, with the last follow-up date ending in December 2022. During this period, all patients maintained the treatment of primary tumor and received the regular monthly infusion of bone metastasis inhibitor drugs. Of the 44 patients, 0 were lost to follow-up, 15 patients died in an average of 16.9 months postoperatively (range 4–45 months) and all caused by cancer, and the remaining 29 patients were followed up for an average of 32.1 months (range 10–60 months).
2.4. Outcome measures
General characteristics: We collected general characteristics on patients at the time of surgery for baseline information comparison, including age, gender, Body Mass Index (BMI), type and progression of primary cancer, surgical side, osteotomy length, operation duration and intraoperative blood loss.
Short-term indicators: Pain is the most visual evaluation indicator in the short term after operation. We collected Visual Analogue Scales (VAS) [8] of patients before and one week after surgery to compare and assess the pain relief from procedure.
Long-term indicators: Functional recovery is the significant evaluation indicator in the long term after operation. To assess hip function in a targeted manner, we selected the universal Harris Hip Score (HHS) [9] as one of our metrics during follow-up. Moreover, since our study was aimed at tumor patients undergoing limb-salvage surgery, we incorporated Musculoskeletal Tumor Society 93 function score (MSTS93) [10] and Toronto Extremity Salvage Score (TESS) [11] into the study. MSTS93 and TESS were originally designed to appraise the life quality of sarcoma patients, but now they have evolved to be applicable to all patients with limb malignancies [7], [12]. MSTS93 consists of 6 sections, each scored 0–5, which translates into a total score between 0 and 100%. TESS consists of 30 questions, each scored 0–5, which translates into a total score between 0 and 100. Lastly, we separately listed the range of motion (ROM) as an independent indicator to demonstrate the activity level of hip joint more directly. Considering the practicality of daily hip activities and the risk of possible prosthetic dislocation during the examination, we focused on flexion, abduction and external rotation of the postoperative hip joint; extension, adduction and internal rotation were not included in our observations.
Complication outcomes: On the one hand we adopted Henderson's classification of 5 failure modes for tumor endoprostheses as major complications, including soft tissue failure (dislocation), aseptic loosening, structural failure, infection and tumor progression [13]. On the other hand, we identified 5 other characteristic complications of hip replacement as minor complications, including hip pain, leg-length discrepancy, surgical site hematoma, deep vein thrombosis and pulmonary embolism [14], [15], [16].
2.5. Statistical analysis
All data from the study were processed with SPSS 21.0 software. For quantitative data, mean and standard deviation (SD) were used to describe, and corresponding t-test was applied for comparative analysis. For categorical data, frequency and percentage were used to describe, and chi-squared test was applied for comparative analysis. All statistical analyses were considered significant at P < 0.05.
3. Results
3.1. General characteristics
As demonstrated in Table 1. This was a cohort of 44 patients with an average age of 65 years and an average BMI of 21.6, comprising 19 male and 25 female. Of these patients with metastatic tumors in the femur, 27 involved the left leg, 17 involved the right leg, and an additional 7 suffered distant metastases outside of the bone, with the highest rate of primary cancer type leading to these metastases being lung cancer (45.5%).
Table 1.
Comparison of patient baseline characteristics at the time of surgery.
| Characteristics | Total, n = 44 |
With eggshell, n = 12 |
Without eggshell, n = 32 |
t | χ2 | P value |
|---|---|---|---|---|---|---|
| Age (yr), mean ± SD | 65.0 ± 8.2 | 61.4 ± 6.4 | 66.3 ± 8.5 | −1.801 | 0.079 | |
| Gender, n (%) | 3.709 | 0.054 | ||||
| Male | 19 (43.2) | 8 (66.7) | 11 (34.4) | |||
| Female | 25 (56.8) | 4 (33.3) | 21 (65.6) | |||
| BMI, mean ± SD | 21.6 ± 2.7 | 22.5 ± 3.2 | 21.3 ± 2.5 | 1.268 | 0.212 | |
| Primary cancer type, n (%) | 8.876 | 0.181 | ||||
| Lung cancer | 20 (45.5) | 3 (25.0) | 17 (53.1) | |||
| Breast cancer | 6 (13.6) | 1 (8.3) | 5 (15.6) | |||
| Liver cancer | 4 (9.1) | 1 (8.3) | 3 (9.4) | |||
| Renal carcinoma | 2 (4.5) | 1 (8.3) | 1 (3.1) | |||
| Colon Cancer | 2 (4.5) | 2 (16.7) | 0 (0) | |||
| Hematologic malignancies | 4 (9.1) | 2 (16.7) | 2 (6.3) | |||
| Others | 6 (13.6) | 2 (16.7) | 4 (12.5) | |||
| Distant metastasis except bone, n (%) | 0.007 | 0.933 | ||||
| Yes | 7 (15.9) | 2 (16.7) | 5 (15.6) | |||
| No | 37 (84.1) | 10 (83.3) | 27 (84.4) | |||
| Surgical side, n (%) | 0.899 | 0.343 | ||||
| Left | 27 (61.4) | 6 (50.0) | 21 (65.6) | |||
| Right | 17 (38.6) | 6 (50.0) | 11 (34.4) | |||
| Osteotomy length (cm), mean ± SD | 17.5 ± 3.8 | 18.3 ± 5.2 | 17.2 ± 3.1 | 0.898 | 0.375 | |
| Operation duration (h), mean ± SD | 3.5 ± 0.7 | 3.6 ± 0.6 | 3.4 ± 0.8 | 0.843 | 0.404 | |
| Intraoperative blood loss (mL), mean ± SD | 719.3 ± 403.5 | 587.5 ± 186.0 | 768.8 ± 452.0 | −1.339 | 0.188 |
In addition, regarding the comparison of age, gender, BMI, primary cancer type, distant metastasis and surgical side, no significant differences were identified between the 12 patients who received the eggshell procedure and the 32 patients who did not. Similarly, the differences in osteotomy length, operative duration and blood loss between the two groups were also insignificant. The application of the eggshell procedure in our patients was not detected to lead to additional intraoperative complications.
3.2. Short-term indicators
As demonstrated in Table 2. The VAS decreased significantly in both groups at one week postoperatively compared with the preoperative VAS (both P < 0.001), but the average VAS decline was stronger in patients with eggshell procedure (50.7%) than in patients without it (30.4%). On the other hand, the comparison of preoperative VAS was not significantly different between the two groups, while the postoperative VAS of patients who received the eggshell procedure was significantly lower than that of patients who did not (P = 0.015). In the short-term evaluation of postoperative pain relief, our eggshell procedure provided an even better performance.
Table 2.
Comparison of patient VAS between pre and postoperative period as well as with and without eggshell procedure (mean ± SD).
| With eggshell, n = 12 |
Without eggshell, n = 32 |
t | P value | |
|---|---|---|---|---|
| Preoperative VAS | 7.1 ± 1.5 | 6.9 ± 1.5 | 0.290 | 0.773 |
| Postoperative VAS | 3.5 ± 0.8 | 4.8 ± 1.7 | −2.524 | 0.015 |
| t | 13.787 | 13.263 | ||
| P value | < 0.001 | < 0.001 |
3.3. Long-term indicators
As demonstrated in Table 3. In the process of long-term follow-up, on the whole, patients who underwent the eggshell procedure presented superior functional recovery and life quality than those who did not. The total scores of HHS (P < 0.001), MSTS93 (P = 0.002) and TESS (P = 0.009) were all significantly higher in patients with eggshell procedure than in patients without it. Specifically, the scores of pain (P = 0.040 and P = 0.042, respectively) and function (both P < 0.001) in HSS and MSTS93 were both significantly different between the two groups. Moreover, patients who received the eggshell procedure had significantly higher scores for deformity (P = 0.004) and range of movement (P < 0.001) in HSS and gait (P < 0.001) in MSTS93 compared to patients who did not. But the scores of emotional acceptance, supports and walking in MSTS93 were not significantly different at the two groups.
Table 3.
Comparison of long-term indicators for patients with and without eggshell procedure (mean ± SD).
| Indicators | With eggshell, n = 12 |
Without eggshell, n = 32 |
t | P value |
|---|---|---|---|---|
| HHS | 83.6 ± 5.8 | 65.5 ± 11.9 | 5.049 | < 0.001 |
| Pain | 41.2 ± 4.0 | 34.3 ± 10.9 | 2.119 | 0.040 |
| Function | 34.7 ± 3.5 | 24.5 ± 3.0 | 9.700 | < 0.001 |
| Deformity | 3.8 ± 0.4 | 3.3 ± 0.5 | 3.071 | 0.004 |
| Range of movement | 4.0 ± 0.3 | 3.3 ± 0.4 | 4.537 | < 0.001 |
| MSTS93 | 76.7% ± 9.0% | 64.8% ± 10.7% | 3.393 | 0.002 |
| Pain | 4.4 ± 0.7 | 3.6 ± 1.3 | 2.094 | 0.042 |
| Function | 3.8 ± 0.5 | 2.8 ± 0.5 | 5.980 | < 0.001 |
| Emotional acceptance | 3.1 ± 1.0 | 3.2 ± 0.8 | −0.243 | 0.810 |
| Supports | 3.8 ± 0.8 | 3.4 ± 0.8 | 1.415 | 0.164 |
| Walking | 4.0 ± 0.7 | 3.6 ± 0.8 | 1.477 | 0.147 |
| Gait | 4.0 ± 0.6 | 3.0 ± 0.7 | 4.533 | < 0.001 |
| TESS | 70.5 ± 7.8 | 64.0 ± 6.7 | 2.722 | 0.009 |
| ROM (°) | ||||
| Flexion | 63.8 ± 4.1 | 61.8 ± 2.5 | 1.895 | 0.065 |
| Abduction | 40.5 ± 2.2 | 29.0 ± 3.2 | 11.447 | < 0.001 |
| External rotation | 32.1 ± 3.3 | 19.3 ± 2.0 | 15.596 | < 0.001 |
In relation to the ROM of hip joint, the differences in flexion angles for the two groups were insufficiently significant (P = 0.065), while both the abduction angles (P < 0.001) and the external rotation angles (P < 0.001) were statistically significantly different between patients who underwent the eggshell procedure and those who did not. Our eggshell procedure, which preserved the greater trochanter with functional musculature attached, brought the patient an improved ROM for hip abduction and external rotation.
3.4. Complication outcomes
As demonstrated in Table 4. For major complications, the incidence of dislocation was significantly lower in patients who received the eggshell procedure than in those who did not (P = 0.039). No prosthetic dislocation occurred at follow-up in patients with eggshell procedure, while dislocation occurred in 9 patients (28.1%) without this procedure, of which 8 received an open reduction and the remaining one was not repositioned. Aseptic loosening and structural failure did not arise in either group of patients. There were also 2 cases of infection and 1 case of tumor progression in the patients who did not undergo the eggshell procedure, while both complications were absent in the patients who underwent it. The incidence of these two indicators was not significant between the two groups.
Table 4.
Comparison of complication outcomes for patients with and without eggshell procedure [n (%)].
| Complications | With eggshell, n = 12 |
Without eggshell, n = 32 |
χ2 | P value |
|---|---|---|---|---|
| Major complications | ||||
| Soft tissue failure (dislocation) | 0 (0) | 9 (28.1) | 4.243 | 0.039 |
| Aseptic loosening | 0 (0) | 0 (0) | ||
| Structural failure | 0 (0) | 0 (0) | ||
| Infection | 0 (0) | 2 (6.3) | 0.786 | 0.375 |
| Tumor progression | 0 (0) | 1 (3.1) | 0.384 | 0.536 |
| Minor complications | ||||
| Hip pain | 0 (0) | 10 (31.3) | 4.853 | 0.028 |
| Leg-length discrepancy | 2 (16.7) | 5 (15.6) | 0.007 | 0.933 |
| Surgical site hematoma | 0 (0) | 1 (3.1) | 0.384 | 0.536 |
| Deep vein thrombosis | 1 (8.3) | 10 (31.3) | 2.444 | 0.118 |
| Pulmonary embolism | 0 (0) | 0 (0) |
For minor complications, the incidence of hip pain was significantly lower in patients who received the eggshell procedure than in those who did not (P = 0.028). No hip pain during daily activities occurred at follow-up in patients with eggshell procedure, while hip pain occurred in 10 patients (31.3%) without this procedure. Pulmonary embolism did not arise in either group of patients. There were also 5 cases of leg-length discrepancy and 1 case of surgical site hematoma in the patients who did not undergo the eggshell procedure, while 2 case of leg-length discrepancy and no surgical site hematoma in the patients who underwent it. The incidence of these two indicators was not significant between the two groups. In addition, regarding deep vein thrombosis, its morbidity was lower in patients with eggshell procedure (8.3%) than in patients without it (31.3%), but the difference was not sufficiently statistically significant (P = 0.118).
Furthermore, any potential specific complications of applying the eggshell procedure, such as possible detachment of the greater trochanter due to too loose cable fixation or possible fracture of the greater trochanter due to too tight cable fixation, were not detected during the follow-up period.
4. Discussion
The eggshell procedure was initially derived from spinal surgery. Although the advent of this procedure was considered creative at the time, its widespread adoption in spinal operation was somewhat limited by its own complexity, excessive complications and unsatisfactory postoperative performance. Given that, we have transferred this concept to PFR surgery, which is convenient and accessible without generating additional complications. In the study, we identified no additional intraoperative complications such as more blood loss and longer operative time in patients with eggshell procedure. At the same time, additional postoperative complications after eggshell procedure, such as tumor progression due to the retained greater trochanter, infection due to the titanium cable as a foreign body, and greater trochanter failure due to the improper fixation were also not observed. Besides, the fact that the muscle insertion was preserved intact and reconstructed together with the greater trochanter, rather than being reconstructed after cutting them off, considerably reduced the surgical side effects, which was evidenced by the significant difference in short-term postoperative VAS between the two groups. More critically, the preserved muscle groups allowed for even better function, which on the one hand improved joint mobility and life quality of patients, as indicated in our study that patients who received the eggshell procedure had significantly higher long-term indicators overall than those who did not. On the other hand, these muscles provided superior protection of the prosthesis against dislocation and hip pain during activity. Dislocation is the most prominent complication of tumor prosthesis [17]. In our study, we discovered that the eggshell procedure significantly decreased the incidence of dislocation as well as hip pain which is a characteristic complication of hip arthroplasty. Our eggshell procedure not only diminished surgical side injuries without adding additional complications, but also improved joint mobility and life quality while reducing the incidence of prosthesis dislocation and hip pain, so it is reasonable to assume that this procedure could be widely disseminated in oncology patients undergoing PFR surgery who meet the indications.
This eggshell procedure is reminiscent of traditional sliding trochanteric osteotomy (STO) to some extent. In contrast to STO, eggshell procedure retains more attachment points for muscles and ligaments, and the physical structure resembling an eggshell guarantees the stability after reconstruction, while on the other hand the design of hollowing out the cancellous bone of the greater trochanter with only the hard cortical bone shell preserved reduces the risk of tumor cell colonization and further growth. Such an advantage is unique for patients with tumors, which may be the reason why no tumor progression or reconstruction failure was observed in patients with eggshell procedure at postoperative follow-up. The PFR surgery performed on tumor patients belongs to palliative care to a certain extent [18]. Meanwhile, the samples we included in the study were uniformly selected from patients with advanced cancer who had developed bone metastases, and the expected survival period is in general not too long. As for these patients, the application of eggshell procedure can facilitate a substantial degree of functional recovery without complications and thus enhances the living standard during their limited postoperative survival. Naturally, this technique is not restricted to patients with metastatic cancer to the femur, but is also applicable to primary femoral sarcoma patients with longer survival period who would require to undergo PFR surgery. Even further, theoretically, our eggshell procedure may be equally effective on other types of joint replacement involving the femur, including THR and total femoral replacement (TFR), as long as the indications are met, which has yet to be proven at a later date.
In terms of the eggshell procedure, we developed the specific indications. As illustrated in Fig. 1A, tumor infiltration theoretically needs to be confined below the lesser trochanter to ensure quality of the preserved greater trochanter and at least 12 cm of tumor distance from the distal femur to ensure stability of the prosthesis inserted into the distal femur. The purpose of establishing indications is mainly to prevent the occurrence of possible local tumor progression in patients after surgery owing to the retention of the greater trochanter invaded by tumor. Nevertheless, since our eggshell procedure only demands the preservation of inactive cortical bone, even if there is slight tumor infiltration in the greater trochanter, local tumor progression may not occur or will not develop rapidly due to the retained greater trochanter. Moreover, given the undesirable postoperative survival duration of certain patients, the necessity of strict adherence to indications is worth being considered.
The eggshell procedure primarily protects and reconstructs the abductors and external rotators of the hip joint. The hip abduction and external rotation mechanisms are secondary in the initiation phase of walking, while they are mainly responsible for pelvic stabilization during single-leg bracing, which if they are deficient translates into a limp pattern known as Trendelenburg gait [7]. This may also explain why there was a significant difference in gait scores but not in walking and support scores between the two groups in our study. The approach to reconstruction of the functional musculature during joint replacement surgery directly determines the outcome of motor function and the stability of artificial prosthesis [19]. The common reconstruction method utilized in hip arthroplasty is to reconnect the muscles to the prosthesis with sutures after cutting them off, but the simple connection rarely ensures that the muscle groups can function adequately [20]. Different from this common method, increasingly cutting-edge techniques are emerging regarding the muscular reconstruction of hip replacement, which basically require the application of corresponding special consumables. Among them, the two most popular options are a prosthesis combined with a bone allograft, the so-called, allograft prosthesis composite (APC), and megaprostheses (MP) with various muscle attachment systems [7], [21]. Apart from these, we also noted that Du et al. confirmed the role of artificial ligaments in the reconstruction of hip periarticular musculature [16]. However, either of the above techniques has its own serious complications leading to adverse outcomes, and more emphatically, the special consumables associated with these techniques are extremely expensive and not always affordable for patients [22]. In contrast, our eggshell procedure has a significant price advantage by eliminating the need for costly consumables and is more accessible to patients, who do not incur excessive additional costs as a result of accepting eggshell procedure.
Our study as a single-center retrospective cohort study still possesses several limitations. The first is that the sample size of the study was too small due to event infrequency. Furthermore, since the included samples were all patients with metastatic tumors, the different primary cancers often led to a differential individualized prognosis, which might affect the outcome measures of the study to some extent. The conclusions remain to be further validated in a more reliable study with multiple centers and large samples.
5. Conclusion
Overall, our eggshell procedure is convenient and accessible, on the one hand reducing surgical side effects without adding additional complications, and on the other improving joint mobility and life quality while decreasing the incidence of prosthesis dislocation and hip pain. Despite it may still remain limitations, we have reasons to believe that this procedure can be further promoted and applied.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
Acknowledgment
Not applicable.
Funding
Not applicable.
Ethics approval and consent to participate
The study was approved by our hospital ethics committee. Informed consent was gained from patients and their families.
Author statement
Jiazheng Zhao collected the data and drafted the manuscript. Xiaowei Ma provided imaging help and reviewed the manuscript. Helin Feng offered academic help and revised the manuscript. All authors confirmed and approved the final manuscript.
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