Combined vertical and horizontal cable fixation of an extended trochanteric osteotomy site

BACKGROUND: The use of an extended trochanteric osteotomy facilitates exposure and aids in the removal of a well-fixed femoral implant and cement during revision total hip arthroplasty. Occasionally, nonunion, fracture, and trochanteric migration have been reported following osteotomy. We evaluated the rate of healing of the osteotomy site and of implant stability when fixation was accomplished with use of vertical trochanteric and horizontal metaphyseal cable fixation (combined cable fixation). METHODS: The clinical and radiographic results of revision total hip arthroplasty with use of an extended trochanteric osteotomy followed by implantation of a distally porous-coated component and combined cable fixation of the osteotomy site in forty-two consecutive patients (forty-three hips) were reviewed. Intraoperative fracture at the osteotomy site occurred in five hips (12%). RESULTS: All osteotomy sites healed by six months, with an average time to union of fifteen weeks. One implant subsided 5 mm in a patient in whom a fracture had occurred at the time of the osteotomy. No trochanteric migration occurred. Two patients required a reoperation: one because of instability, and another because of recurrent infection. CONCLUSIONS: The extended trochanteric osteotomy facilitates revision of a well-fixed femoral component. Despite occasional intraoperative fracture at the osteotomy site, combined vertical trochanteric and horizontal metaphyseal cable fixation resulted in an excellent rate of healing and implant stability.     

Intramedullary rod and cement static spacer construct in chronically infected total knee arthroplasty

Two-stage reimplantation, with interval antibiotic-impregnated cement spacer, is the preferred treatment of prosthetic knee joint infections. In medically compromised hosts with prior failed surgeries, the outcomes are poor. Articulating spacers in such patients render the knee unstable; static spacers have risks of dislocation and extensor mechanism injury. We examined 58 infected total knee arthroplasties with extensive bone and soft tissue loss, treated with resection arthroplasty and intramedullary tibiofemoral rod and antibiotic-laden cement spacer. Thirty-seven patients underwent delayed reimplantation. Most patients (83.8%) were free from recurrent infection at mean follow-up of 29.4 months. Reinfection occurred in 16.2%, which required debridement. Twenty-one patients with poor operative risks remained with the spacer for 11.4 months. All patients, during spacer phase, had brace-free ambulation with simulated tibiofemoral fusion, without bone loss or loss of limb length.     

A modified cement spacer technique for infected total hip arthroplasties with significant bone loss

Complications related to femoral spacers are common during addressing infected total hip arthroplasties by 2-stage revision. We evaluated 11 patients who had 2-stage revisions with massive bone loss after removal of the infected components by a trochanteric osteotomy. All femoral cement spacers were assembled on intramedullary nails. Femurs were protected by a plate, whereas acetabuli were augmented by a cage or roof ring depending on the remaining bone stock. This additional hardware was covered with antibiotic-impregnated cement. Infection was eradicated in 10 (90.9%) of 11 patients within 3.5 months in average. None of the patients had spacer fracture, periprosthetic fracture, or dislocation. Augmentation by hardware covered with antibiotic-impregnated cement is effective and may reduce complications until definitive treatment is performed.     

髋关节置换术后迟发性感染的诊断与治疗

目的探讨髋关节置换术后迟发性感染的诊断和治疗方法。方法对1998年3月至2004年4月收治的11例髋关节置换术后迟发性感染病例进行回顾性分析。男4例,女7例;年龄49￣81岁,平均66岁。11例患者均有疼痛症状,感染距初次手术的时间9￣96个月,平均25.5个月。5例有窦道,8例C反应蛋白增高,9例血沉增快,10例X线片有包括骨溶解、假体松动、新骨形成等阳性表现;行窦道造影检查2例,均发现窦道的近端与关节假体相通。关节穿刺1例,细菌培养结果阴性,术中取标本行细菌培养仍为阴性;同位素99mTc骨扫描1例,发现围绕假体周围均匀的放射性核素浓聚;细菌培养阳性9例,阴性2例。一期翻修8例,其中普通骨水泥固定1例,抗生素骨水泥固定7例;二期翻修3例,在取出假体、彻底清创后,分别放置了三种临时假体间隔器(抗生素骨水泥团、庆大霉素链珠、多孔可灌注Spacer各1例),感染控制后,安放翻修假体,抗生素骨水泥固定。结果术中股骨干骨折1例,无关节脱位、神经血管损伤、静脉血栓等并发症发生。11例患者的感染都得到控制,随访8～72个月,平均29.3个月,感染未见复发。结论髋关节置换术后迟发性感染尚无100%的特异性检查,需要对患者的病史、体征及实验室检查、影像学检查、病原学以及病理学检查结果进行综合分析,才能作出正确的诊断;根据个体情况,选择相应的手术方式是治疗成功的关键。     

全髋关节翻修术中大转子粉碎性骨折或截骨不愈合的治疗

目的 探讨在全髋关节翻修术中采用张力带方法治疗大转子粉碎性骨折或截骨不愈便的临床效果。方法 1992年1月～1998年10月，对295例行全髋关节翻修术中大转子粉碎性骨折或截骨不愈合的19例(20髋)患者进行治疗，男7例．女12例；年龄63～76岁，平均69岁。20髋中，16髋为假体松动伴骨溶解在翻修术中发生股骨大转子骨折，4髋为全髋关节置换时采用股骨转子截骨入路。因转子截骨不愈合致髋外展肌力不足而行翻修术。采用多枚克氏针加张力带钢丝固定的方法进行治疗。结果 术后随访12～118个月,平均30个月。Harris髋关节评分从术前的平均45分恢复至随访时的平均89分。19髋达一期愈合，1髋固定失败后再次行大转于张力带固定后愈合。19髋平均愈合时间为166周。所有病例术后均无髋关节脱位。结论 在全髋关节翻修术中使用多枚克氏针加张力带钢丝固定的方法治疗股骨大转子骨折或截骨不愈合，可以提高愈合率，维持正常的髋关节外展肌功能。该方法也适用于大转子粉碎性骨折或骨质疏松的患者。     

应用抗生素骨水泥间隔体二期翻修治疗人工全膝关节置换术后迟发感染

目的探讨应用抗生素骨水泥间隔体二期翻修治疗人工全膝关节置换术后迟发感染的临床疗效。方法 2007年1月-2009年12月,收治23例(23膝)人工全膝关节置换术后迟发感染患者。男15例,女8例;年龄43～75岁,平均65.2岁。置换术后至出现感染时间为13～52个月,平均17.3个月;发生感染至入院翻修时间为15 d～7个月,平均2.1个月。一期清创、取出假体,植入含庆大霉素抗生素骨水泥间隔体;8～10周感染控制后二期植入假体。分别采用美国特种外科医院(HSS)评分及膝关节学会评分系统(KSS)评价翻修前后患膝功能,并统计总体感染控制率。结果术后患者切口均Ⅰ期愈合。2例二期翻修术后发生再感染,余21例感染控制,总体感染控制率91.3%。患者均获随访,随访时间2～5年,平均3.6年。HSS评分由术前(60.6±9.8)分提高至末次随访时(82.3±7.4)分,KSS评分由术前(110.7±9.6)分提高至末次随访时(134.0±10.5)分,手术前后比较差异均有统计学意义(P<0.01)。X线片复查示假体位置良好,无松动、断裂、假体周围透亮影等异常表现。结论应用抗生素骨水泥间隔体二期翻修能有效控制人工全膝关节置换术后迟发感染,并能较好恢复患膝功能。     

Antibiotic-impregnated cement spacer versus antibiotic irrigating metal spacer for infection management after THA

We prospectively compared the effects of an antibiotic-impregnated cement spacer and an antibiotic irrigating metal spacer in the treatment of infections after total hip arthroplasty (THA) to determine a better method for 2-stage revision of infected THA. We used a uniform protocol of a 3-month spacer interval and specific local and systemic antibiotic therapies. The clinical outcome was determined by assessing operation time, blood loss during spacer implantation, hospital stay and time in bed, and joint function. The patients were followed for a mean 61.4 months (range, 24-94 months). Antibiotic-impregnated cement spacers had a higher rate of infection control than antibiotic irrigating metal spacers (96.2% vs 76%, respectively; P<.01), with no recurrence of infections or implant loosening. Patients receiving antibiotic-impregnated cement spacers had a shorter operation time (2.42±0.65 vs 3.34±0.36 hours metal spacers; P<.01), less blood loss (1085.48±279.49 vs 1964.78±469.23 mL metal spacers; P<.01), a shorter hospital stay (24.53±4.72 days vs 51.36±3.46 days metal spacers; P<.01), and better function before the second step of the 2-stage revision (Harris Hip Score, 88.16±6.94 vs 79.54±6.48 metal spacers; P<.05), and they were free from long-term irrigation. Compared with the antibiotic irrigating metal spacer, the antibiotic-impregnated cement spacer is characterized by higher infection control rate, better joint function recovery before the second operation, shorter operation time, and less blood loss, with no continuous irrigation required.     

Extended slide trochanteric osteotomy for revision total hip arthroplasty

BACKGROUND: The purpose of this study was to assess the rate of union, time to union, and complications associated with the extended slide trochanteric osteotomy. We also evaluated how outcomes were influenced by the preoperative cortical-bone thickness, the preoperative cancellous-bone quality of the greater trochanter, the number of cables used to reattach the trochanteric osteotomy fragment, and the use of cortical strut augmentation. METHODS: We reviewed the results for forty-six hips in forty-five patients who underwent a revision total hip arthroplasty with an extended slide trochanteric osteotomy between December 1991 and December 1996. Twenty-three patients were men, and twenty-two were women; the mean age at the time of the operation was 66.3 years. Two hips had an isolated acetabular revision, fifteen had an isolated femoral revision, and twenty-nine had acetabular and femoral revisions. One patient (one hip) was lost to follow-up. RESULTS: At a mean of forty-four months after the operation, the rate of union of the distal osteotomy site was 98 percent (forty-four of forty-five hips), with no change in the femoral component position. The time to union was not significantly correlated with the number of cables, the preoperative cortical-bone thickness, or the preoperative cancellous-bone quality of the greater trochanter. Interestingly, the time to bridging-callus union was significantly longer in the hips with a strut allograft than in the hips without a strut allograft (p = 0.04, t test for independent samples). Two fractures of the osteotomy fragment occurred, but neither necessitated another revision. CONCLUSIONS: The extended slide trochanteric osteotomy allows extensive acetabular and femoral exposure, facilitates removal of distal cement or a well fixed porous-coated stem, and allows reliable reattachment and healing of the trochanteric fragment.     

The Use of Extended Trochanteric Osteotomy in 2-Stage Reconstruction of the Hip for Infection

BackgroundThe effect of extended trochanteric osteotomy (ETO) with immediate cerclage wire fixation on the scene of chronic periprosthetic joint infection on infection eradication and the osteotomy healing remains unclear.MethodsOne hundred seventeen patients who underwent two-stage revision total hip arthroplasty for chronic periprosthetic joint infection were enrolled in the study. The minimum follow-up was 2 years. Of these, 48 patients had underwent ETO and immediate cerclage wire fixation during the first-stage surgery, while 69 did not undergo ETO or any other osteotomy. In addition, 18 patients had underwent ETO in the second-stage reimplantation surgery. Repeated debridement, curative rate of infection, and complications were compared between the 2 groups. Meanwhile, osteotomy healing between the first and second osteotomy were also compared.ResultsThe repeated debridement rate and curative rate of infection were 2.1% and 95.8% in the ETO group, compared with 13.0% and 82.6% in the non-ETO group; there were significant difference between the 2 groups in these parameters (P = .037 and .030, respectively). Meanwhile, osteotomy healing rate was 93.8% in first-stage surgery with infection scene and 100% in second-stage surgery without infection; no significant difference was detected in osteotomy healing rate and time to healing (P = .278 and .803, respectively). The rate of complication was similar in both groups.ConclusionsETO combined with immediate cerclage wire fixation does not appear to reduce the rate of infection eradication. There was no harmful effect on complication rate and osteotomy healing.     

术中自制抗生素骨水泥占位器在治疗髋关节置换术后感染的并发症研究

目的:研究术中自制抗生素骨水泥占位器在治疗髋关节置换术后感染的控制率及其并发症。方法 :对2006年1月至2016年7月解放军总医院骨关节科髋关节置换术后感染行占位器植入患者265例(266髋)进行回顾性研究,其中男143例(144髋),女122例(122髋)。占位器均利用自行设计的压模器术中制作,全部占位器均加入万古霉素,同时根据细菌药敏结果加入另外一种抗生素。记录是否行大粗隆延长截骨术(ETO)取出感染假体、占位器并发症(断裂和脱位)的发生率、Harris评分和感染的控制率。结果:占位器植入时患者的平均年龄(57.4±14.2)岁。39例(14.7%)行ETO取出感染假体。38例(14.3%)出现了占位器的并发症,其中28例(10.5%)出现了占位器断裂,10例(3.8%)出现了占位器脱位。平均随访时间(83.4±14.6)个月。Harris评分从术前的47.56±14.23上升到末次随访的86.43±12.84(P0.05)。256例(96.6%)植入占位器术后感染得到了有效控制。Ⅱ期翻修术后到末次随访,4例患者再次出现感染,并再次行Ⅱ期翻修,感染得到控制。感染总的控制率为95.1%(252/265)。结论:术中自制抗生素骨水泥占位器控制髋关节置换术后感染具有显著效果,占位器并发症发生率较低,占位器结合钢丝、钛缆、捆绑带、异体骨板及螺钉不影响感染的控制。     

New uses for gentamicin-impregnated polymethyl methacrylate spacers in two-stage revision hip arthroplasty

The use of antibiotic-impregnated cement as a bone spacer in two-stage revision hip surgery has been well described. Two additional placements for spacers are described: within the trochanteric osteotomy and overlying the greater trochanter. These spacers have been found to dramatically facilitate exposure at the second-stage procedure and are now being incorporated into all two-stage revision hip arthroplasties at The General Infirmary at Leeds.     

Extended trochanteric osteotomy via the direct lateral approach in revision hip arthroplasty

A review of the results of the extended trochanteric osteotomy through a modified direct lateral approach in revision total hip arthroplasty was done. We reviewed 44 patients (45 procedures) at a minimum of 2 years followup (mean, 3.8 years; range, 2.1-7.2 years). There were 26 men and 18 women with a mean age at the time of surgery of 70.8 years (range, 36.9-90.4 years). Indications for use of the trochanteric osteotomy included facilitation of cement removal (25 procedures), proximal femoral varus deformity (14 procedures), trochanteric malposition (five procedures), and previous trochanteric osteotomies with significant bony overgrowth (three procedures). The mean length of the osteotomy was 133.9 mm. The mean migration of the osteotomized fragment was 2.1 mm (range, 0-20 mm) with significantly more proximal migration seen with the use of cerclage wires when compared with cables. There were two cases of trochanteric escape, for which the patients required repeat open reduction internal fixation. There were two late fractures of the greater trochanter. One femoral component had early subsidence for which the patient required re-revision with a further extended trochanteric osteotomy. The mean time to union of the remaining 40 hips was 10.3 months (range, 6-24 months). There only was one dislocation postoperatively. The extended trochanteric osteotomy through the modified direct lateral approach in revision total hip arthroplasty is a reproducible and reliable technique with a lower dislocation rate but a higher incidence of trochanteric fracture and escape than previously described with its use in the posterior approach.     

Cement spacer loaded with antibiotics for infected implants of the hip joint

It is difficult to treat infected implants of the hip joints. Such treatment involves immeasurable physical and psychological suffering of the patients. We used antibiotic-impregnated cement spacers in 17 cases of infection after total hip arthroplasty and bipolar arthroplasty with good clinical results. We thoroughly removed any foreign material and formed an antibiotic-impregnated cement spacer into a similar shape as that of the implants. A cement spacer enables high-concentration antibiotics to act on infected sites. Also, it can prevent leg length discrepancy and atrophy of bones or muscles. Although cement spacers have been reported to have problems regarding shape and strength, we achieved good results with a cement spacer mold in the present study. No recurring infection has been found at a mean follow-up period of 3 years and 2 months.     

Application of temporarily functional antibiotic-containing bone cement prosthesis in revision hip arthroplasty

Purpose

To investigate the clinical outcome of two-stage revision total hip arthroplasty for infected hip arthroplasty using antibiotic-impregnated cement prosthesis.

Materials and methods

Forty-one patients, who suffered from an infection after hip replacement or internal fixation of femoral neck and trochanteric fractures, were treated with a two-stage revision hip arthroplasty and followed up for an average of 37 months. All the patients were implanted with antibiotic-impregnated cement prosthesis as one-stage treatment and were then managed with two-stage revision hip arthroplasty after 12–24 weeks. During the follow-up, Merle d’Aubigné hip score and Harris score were employed for assessment of hip function, and infection recurrence was observed.

Results

According to Merle d’Aubigné hip score, 16 patients (39.2 %) were excellent, 19 (46.3 %) were good, 6 (14.6 %) were moderate, and no bad result and the average score was 15.42. Mean Harris score of preoperation, interval period, and postoperation was 46.7, 66.5, and 92.3, respectively. There was no infection recurrence.

Conclusion

Two-stage revision total hip arthroplasty for infected hip arthroplasty using antibiotic-impregnated cement prosthesis has a satisfying clinical outcome.     

Treatment of comminuted trochanteric fractures and non-union of trochanteric osteotomy in revision total hip arthroplasty

To explore the clinical efficacy of thetreatment of comminuted trochanteric fractures andtrochanteric osteotomy non-union in revision total hiparthroplasty with tension-band f‘Lxation.     

大转子延长截骨钢丝固定结合自体骨屑植骨在全髋关节翻修术中的应用

目的: 探讨采用大转子延长截骨钢丝固定加自体骨屑植骨进行全髋关节置换翻修的临床效果。方法: 自2010年12月至2018年12月,应用大转子延长截骨钢丝固定结合自体骨屑植骨,行全髋关节置换翻修术患者18例,其中男8例,女10例;年龄68~82(78.89±3.32)岁;初次置换术后至翻修时间9~22(16.33±2.93)年。术后定期随访记录患者截骨块愈合时间、完全负重活动时间、髋关节Harris评分及并发症等情况。结果: 纳入研究的18例患者均获得随访,时间16~38(25.78±6.65)个月。手术切口均Ⅰ期愈合。切口长度16~21(18.89±1.32) cm。手术时间105~128(115.44±6.59) min;出血量240~285(267.44±13.77) ml。截骨块愈合时间12~18(15.61±1.75)周;患者完全负重活动时间14~22(17.78±2.53)周。术前髋关节Harris评分(47.11±5.04)分,完全负重活动时髋关节Harris评分(76.39±3.85)分,末次随访时髋关节Harris评分(82.22±2.76)分,差异有统计学意义(P<0.05)。随访期间,患者均未发生患肢短缩、感染、切口愈合不良、假体松动及下沉、假体周围骨折等并发症。结论: 在全髋关节置换翻修术时,应用大转子延长截骨钢丝固定结合自体骨屑植骨,能够获得满意的临床治疗效果,但需要术者对翻修术前、术中及术后恢复等各个时期做好系统规划。     

Long-term results and complications of cement augmentation in the treatment of unstable trochanteric fractures

Thirty-eight patients with unstable trochanteric fractures of the femur were treated with Dimon-Hughston displacement osteotomy and cement augmentation at the fracture site. Of these patients 76 per cent had excellent and good results after an average follow-up of 3.7 years (range 2-5 years). Late complications occurred in six hips. These included non-union at the trochanteric fracture, protruding pin, partial destruction of the femoral head, subcapital fracture of the femoral neck, and avascular necrosis of the femoral head. All complications occurred late (1 year after surgery) and were related to inappropriate placement and excessive amount of cement, together with inadequate new bone formation. The augmentation of cement provided early stability for early mobilization in these elderly patients. However, when improperly used, late complications can occur.     

The outcome of trochanteric reattachment in revision total hip arthroplasty with a Cable Grip System: mean 6-year follow-up.

We have reviewed 251 hips that were revised by the senior authors with subsequent reattachment using the Dall-Miles Cable Grip System. Of these patients, 223 were available for follow-up. A trochanteric slide osteotomy was used for most cases (n = 170), and the remainder had conventional trochanteric osteotomy to facilitate surgical exposure. Follow-up period was 1 to 8 years. Forty-eight percent (n = 108) of the hips had a previous trochanteric osteotomy. Thirteen percent (n = 30) had a prior trochanteric nonunion. Of the 223 hips, 91% (n = 204) of the trochanters remained attached to the trochanteric bed when reapproximated by the cable grip system. The 2 multifilament cables were passed medially through drill holes in the lesser trochanter in 67% (n = 149) of cases. Of the hips, 16% (n = 35) had 2 cables passed through bone lateral to the prosthesis, and 17% (n = 39) had cables passed 1 medial and 1 lateral to the prosthesis. Cable breakage was noted in 10% (n = 23) of cases. Of those 23, 70% (n = 16) were stainless steel. Unraveling of the cable occurred in 18% (n = 41) of cases. There were 19 nonunions (9%). Of the 19 nonunions, 74% (n = 14) were stainless steel. The trochanter was reattached to bone in 9 hips, to cement in 4 hips, and to a proximal femoral allograft in 6 hips (P = .0001). Eight of the 19 hips (42%) had the cables placed lateral to the prosthesis (P = .0002). When bone-to-bone apposition was achieved at surgery, the nonunion rate was 4%. In this difficult group of revision procedures, the Dall-Miles Cable Grip has provided reliable trochanteric fixation. Factors associated with successful trochanteric healing include use of vitallium cables, use of a trochanteric slide osteotomy, cables passed medially through the lesser trochanter, cerclage rather than intramedullary placement, and bone-to-bone apposition.     

大转子延长截骨在全髋关节翻修术中应用的临床评价

目的 回顾性研究采用大转子延长截骨(extended troehanteric osteotomy,ETO)行全髋关节翻修术后股骨柄的位置变化,评价ETO在股骨假体稳定件髋关节翻修术中的作用.方法 1998年1月至2007年6月,采用ETO对股骨柄或骨水泥壳固定稳定性全髋关节33例33髋进行翻修.翻修术后采用Harris评分和MOMAC评分评估髋关节功能,摄动态X线片观察截骨块愈合、假体位置改变及股骨柄与股骨髓腔匹配等情况.结果 25例随访12～103个月,平均63个月.Harris评分由术前平均38.4分,提高到末次随访时88.7分;WOMAC评分由术前平均56.2分,降至末次随访时42.8分.大转子截骨块均在术后4～10个月骨性愈合.3例发生股骨柄下沉.平均3.4mm.股骨柄假体出现外翻、内翻各1例.无术中或术后骨折、钢丝断裂、感染、假体周围骨溶解以及异位骨化发生.术后关节脱位1例.结论 对假体固定稳定性股骨柄进行翻修,采用ETO有利于假体的安全取出,术后截骨块愈合率高,延长截骨不影响假体稳定性.股骨柄下沉、位置改变、截骨块骨折等并发症发生率低.     

The Influence of Spacer Design on the Rate of Complications in Two-Stage Revision Hip Arthroplasty

BackgroundAntibiotic cement spacers are used during 2-stage revision total hip arthroplasty for prosthetic joint infection. Complications including dislocation and periprosthetic fracture have been reported but a large cohort comparing spacer design features is lacking. We aimed to determine if spacer design is associated with perioperative complications.MethodsWe performed a retrospective review of antibiotic cement spacers implanted between 2004 and 2014. Radiographic assessment included leg length, offset, and bone loss (Paprosky classification). Clinical outcomes included dislocation, periprosthetic fracture, spacer fracture, infection cure, and overall reoperation rate. Univariate analysis, Student’s t-test, chi-squared test, or Kruskal-Wallis test was employed (P < .05).ResultsOne hundred eighty-five patients were treated: 42% were female and mean age was 64 years (range 24-93, standard deviation 13.6). Spacer types were (1) molded (53%), (2) antibiotic-coated prosthesis (30%), (3) handmade (12%); and (4) prefabricated (4%). Cemented acetabular liners were used in 3% (6/185). There was no loss to follow-up during the interstage period. Spacer complications occurred in 26% (48/185). Dislocation occurred in 9% (17/185) and was associated with reduced femoral offset of >5 mm (P = .033) and increased bone loss (P = .01). Spacer fracture occurred in 8% (14/185); 12% (12/97) molded versus 8% (2/23) handmade (P = .02). Periprosthetic femur fracture was associated with increased offset >5 mm (P = .01) and extended trochanteric osteotomy (P = .001).ConclusionDuring 2-stage total hip arthroplasty, antibiotic-loaded cement spacers had an overall complication rate of 26%. Spacer design, acetabular and femoral bone loss, and offset restoration were significantly associated with perioperative complications. We recommend the optimization of antibiotic-loaded cement spacer placement to minimize potential complications by focusing on restoration of leg-length and offset, ensuring adequate femoral fixation and paying attention to selection of an appropriate head/neck ratio.